Stephen Mascaro is developing sensors that can measure blood flow patterns in the human fingertip. These fingernail sensors may one day be used to control robots and operate computers in a novel and ergonomic way. An assistant professor in the Department of Mechanical Engineering, Dr. Mascaro is also director of the Biorobotics Laboratory at the University of Utah.

He cites, for one example, the potential use of fingernail sensors in factory settings so that humans and robots may safely and efficiently work together. A factory worker would wear the fingernail sensors, and as he or she works on an assembly line, the robot would know when to step in and execute its part.

“Imagine a situation where you take the best qualities of both humans and robots and put them together to accomplish a task,” says Dr. Mascaro.

The key to effective human-robot interaction, Dr. Mascaro says, is that the robot knows exactly what the worker’s hands are doing at all times. This is where the idea for fingernail sensors comes in.

Fitted onto a person’s fingernails, the sensor devices project light into the fingernails to measure color change, and therefore, blood flow. As a person presses down or slides a finger on a surface, the patterns of color in the fingernail change. The sensors can detect those patterns and accurately measure movement, direction, and force, while relaying that information to the robot.

The sensors are built on rigid circuit boards printed with lines of metal conductors and implanted with light-emitting diodes that shine light into a fingertip. To read blood flow properly, the sensor must be customized to each individual fingernail’s size and shape, making mass production of the sensors impossible.

To get around the need for customization, Dr. Mascaro is developing silicone rubber sensors that would accurately read blood flow, but could fit any size or shape fingernail.

The other challenge is the need to individually calibrate the sensors to properly use them. Dr. Mascaro and his associates are working on developing a mathematical model – or set of equations that relate force and motion of the finger to the sensor signals – that will automatically calibrate the sensors for each individual. “We hope to find one equation that fits everybody, so we won’t have to do extensive calibration every time,” he says.

In related research, Dr. Mascaro is working with Professor John Hollerbach in the School of Computing to develop software and a video camera that would measure color patterns in the fingernail without the need to wear sensors. Funded by the National Institutes of Health, this project would potentially allow for the development of virtual computer keyboards and mouses. Within view of a camera, an individual’s finger would apply slight pressure to a hard surface to make the cursor on a computer move, and the individual would type on a hard surface to make letters appear on the computer screen.

Because such a small amount of movement and pressure would be needed to make the virtual keyboard and mouse work, such research would potentially be invaluable to people with carpal tunnel syndrome or other repetitive-motion injuries.

“The slightest touch changes fingernail coloration, so a person wouldn’t have to push very hard,” he says. “And you could touch anywhere – on your desktop or on your screen.”

Dr. Mascaro also sees the potential of applying the camera idea to fingernail sensors, in effect making a wearable video camera that reads fingernail blood flow. Consequently, a person wouldn’t have to worry about maintaining line of sight with a detached video camera.

Other research in Dr. Mascaro’s biorobotics lab involves making robots more humanlike. Inspired by the way humans move, he is developing robotic “muscles” made from shape-memory titanium alloy wires that contract when heated and expand to their original shape when cooled – similar to how human muscles flex and relax.

Individually encased in rubber tubes, each shape-memory wire – only a fraction of a millimeter in diameter – is heated and cooled alternately with hot and cold water running through the tube. Several strands of wires make up one robotic muscle.

“The wires can contract only about 4 percent of their length, which is 20 percent of what a human muscle can do,” says Dr. Mascaro. “On the other hand, they can exert about two hundred times the force of a human muscle for the same size. And we can leverage that power with gears or pulleys to achieve the same amount of movement as a human limb.”

Powering the muscles with electricity is extremely inefficient, so Dr. Mascaro and his associates are designing and building a cardiovascular system – starting with a robotic heart that will work to alternately pump hot and cold water to the wires. The heart is also being designed with shape-memory wires, so that the chambers of the heart can self-sufficiently contract and extend to circulate the fluid throughout the robotic body (similar to how a human heart pumps blood to the extremities).

“Right now, our robotic heart is only pumping enough fluid to keep itself going and nothing more,” says Dr. Mascaro. “So our research involves getting more output from it.”

As he advances the basic science of robotics, Dr. Mascaro hopes his research will someday provide the building blocks to enable robots to do things never before feasible, possibly even in the area of national defense. “Maybe someday small muscle-actuated robots could silently go into caves and hunt down terrorists,” he says. “But we’re still a long way away from using this technology in real world applications.”

For more information, please visit the Biorobotics Laboratory web page.

Learn more about Dr. Stephen Mascaro.