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Stanford Report, April 2, 2003

Haptic technology simulates the sense of touch -- via computer Tactile interface lets surgeons make 'incisions'; computer gamers feel their golf drives


Anyone who thinks a pinch means they aren't dreaming hasn't tried haptics. J. Kenneth Salisbury Jr., research professor of computer science and of surgery, develops tools that allow people to touch --poke, squeeze, stroke and heave -- the objects they see on their computer screen.

Haptics, the science of touch, lets computer users interact with virtual worlds by feel. Some commercial computer games already benefit from early haptic devices, like the force-feedback steering wheels that torque and vibrate on bumpy driving-game roads. But haptics isn't all fun and games. Scientists use computers to simulate not only the impact of a golf club hitting the ball, but also the springiness of a kidney under forceps, the push of an individual carbon nanotube in an atomic force microscope and the texture of clothing for sale on the Internet.

Graduate student François Conti demonstrates a device that lets computer users feel and manipulate the objects depicted on their screens. This spider-like robot can take tactile "pictures." In the lab of Kenneth Salisbury, professor of computer science and of surgery, Conti and other researchers explore haptics -- the science of touch. Photo: L.A. Cicero

Using Salisbury's haptic technology is like exploring the virtual world with a stick. If you run your stick along a cyberspace sidewalk, it vibrates lightly. If you push it into a virtual balloon, you feel the balloon push back. The computer communicates sensations through a haptic interface -- a stick, scalpel, racket or pen that is connected to force-exerting motors.

"By coordinating the forces that are exerted on your handle or your stick or your stylus or your fingertips, you can make it feel as though you're touching something," says Salisbury.

Touch is an unusual sense in that it goes two ways. Haptic interfaces can communicate the contours of a sculpture, and they can apply pressure to sculpt. SensAble Technologies Inc., a spinoff from work Salisbury and colleagues did when he was at the Massachusetts Institute of Technology, commercialized one such haptic interface in 1993. Designers have used it to carve out of thin air products from Nike shoe soles to Chicken Run collectibles.

Salisbury's Stanford lab also uses a haptic interface from ForceDimension, a company co-founded by graduate student Francois Conti. Conti is using one such device to take tactile "pictures." The spiderlike robot handle presses on a surface and records the forces causing deformation. It can then play back the forces it experienced and make a person holding the handle feel like he's poking the surface himself.

Gaming is one of the first applications of haptics that is being realized. Two students in Salisbury's experimental haptics course last spring programmed a forceful version of virtual ping-pong they called "Haptic Battle Pong." Interest in the game caused an Internet traffic jam that shut down the haptic interface manufacturer's website for a day.

Also in the works is simulated surgery. Just as commercial pilots train in flight simulators before they're unleashed on real passengers, surgeons will be able to practice their first incisions without actually cutting anyone. Simulation for surgical training is a major focus in Salisbury's lab. This work is funded by the National Institutes of Health and Stanford's Bio-X Program.

Creating a realistic, interactive internal organ is no easy feat. "It's not just something that you can touch and say, 'OK, it's round and it's squishy and it's got a bump here,' but something that you can then cut and it will bleed, or sew and it will stop bleeding," Salisbury says.

A liver is more complicated to model than is a ping-pong ball. For a ball, all you have to tell the computer is how soft or hard it is, how sticky or smooth, how stretchy, how dense. One value for each will do the trick. But a liver may get stiffer as you stretch it, or be more elastic in one direction than another. A healthy liver may feel nice and slippery, and a sick liver, not. And modeling the organ in real time, so that the image deforms when you poke it and not a second later, runs up against the limits of computing power.

Go ahead -- squeeze the Charmin

Opposable thumbs are the next step in the evolution of computer haptics. Grasping is a much more natural way to interact with the virtual world. In May, postdoctoral researcher Federico Barbagli will travel to the International Conference on Robotics and Automation in Taiwan to present the Salisbury lab's most recent gripper.

The gripper consists of little haptic hats for the thumb and forefinger. With this new two-fingered haptic interface, researchers can pick up a virtual block, and then let it slip controllably between their fingers. That feat requires a degree of finesse, Salisbury says, that simply was not possible before.

The new gripper also has the advantage of being transparent. "A well-designed haptic device is one that makes you feel a contact when you're touching something in the virtual environment, and magically disappears when you're not touching anything," Barbagli says.

Eventually, surgeons will sew virtual stitches with two hands, and virtual surgery will take on an unprecedented degree of realism. "People will really begin to feel like they're holding the tissue and they're tearing it," Salisbury says. "And they'll feel bad about it because they squeezed too hard."

Jessica Ruvinsky is a science writing intern at the Stanford News Service.


Kenneth Salisbury

























The computer communicates sensations through interfaces such as the PHANTOM™ Haptic Interface, produced by SensAble Technologies, Inc. of Woburn, Mass.