Building a robot with human touch

Advances in haptics and kinematics are essential if robots are ever to collaborate with humans

In factories and warehouses, robots routinely outdo humans in strength and precision. Artificial intelligence software can drive cars, beat grandmasters at chess and leave ‘Jeopardy!’ champions in the dust.

But machines still lack a critical element that will keep them from eclipsing most human capabilities anytime soon: a well-developed sense of touch.

Consider Dr Nikolas Blevins, a head and neck surgeon at Stanford Health Care who routinely performs ear operations requiring that he shave away bone deftly enough to leave an inner surface as thin as the membrane in an eggshell.

“Being able to do virtual surgery, you really need to have haptics,” he said, referring to the technology that makes it possible to mimic the sensations of touch in a computer simulation.

The software’s limitations typify those of robotics, in which researchers lag in designing machines to perform tasks that humans routinely do instinctively. Since the first robotic arm was designed at the Stanford Artificial Intelligence Laboratory in the 1960s, robots have learned to perform repetitive factory work, but they can barely open a door, pick themselves up if they fall, pull a coin out of a pocket or twirl a pencil.

The correlation between highly evolved artificial intelligence and physical ineptness even has a name: Moravec’s paradox, after the robotics pioneer Hans Moravec, who wrote in 1988, “It is comparatively easy to make computers exhibit adult-level performance on intelligence tests or playing checkers, and difficult or impossible to give them the skills of a 1-year-old when it comes to perception and mobility.”

Advances in haptics and kinematics, the study of motion control in jointed bodies, are essential if robots are ever to collaborate with humans in hoped-for roles like food service worker, medical orderly, office secretary and health care assistant. 

“It just takes time, and it’s more complicated,” Ken Goldberg, a roboticist at the University of California, Berkeley, said of such advances. “Humans are really good at this, and they have millions of years of evolution.”

Touch is a much more complicated sense than one might think. Humans have an array of organs that allow them to sense pressure, sheer forces, temperature and vibrations with remarkable precision. 

Research suggests that our sense of touch is actually several orders of magnitude finer than previously believed. Last fall, for example, Swedish scientists reported in the journal Nature that dynamic human touch — for example, when a finger slides across a surface — could distinguish ridges no higher than 13 nanometers, or about 0.0000005 of an inch.

Stacking blocks may seem like an easy task for a human, but robots have long struggled with such fine control. HDT’s Adroit manipulator uses force-sensing and vision to accomplish the delicate task. In the case of tiny surface variations, cues come from Pacinian corpuscles, oval-shaped structures about a millimeter long (one twenty-fifth of an inch) that signal when they are deformed.

Science of ‘haptics’

Replicating that sensitivity is the goal of haptics, a science that is playing an increasing role in connecting the computing world to humans. One of the most significant advances in haptics has been made by Mako Surgical, founded in 2004 by the roboticist Rony Abovitz. In 2006, Mako began offering a robot that provides precise feedback to surgeons repairing arthritic knee joints.

“I thought haptics was a way to combine machine intelligence and human intelligence in a way that the machine would do what it was good at and the human would do what the human was good at, and there was this really interesting symbiosis that could come about,” 

 Abovitz said, adding: “The surgeon still has the sense of control and can put the energy into the motion and push. But all of the intelligent guidance and what you thought the surgeon would normally do is done by the machine.”

Even in industries where robots are entrenched, experts worry about the dangers they pose to the people who work alongside them. Robots have caused dozens of workplace deaths and injuries in the United States; if a robot revolution is ever to take place, scientists will have to create machines that meet exacting safety standards — and do it inexpensively.

“For the last 30 years, industrial robots have focused on one metric: being fast and cheap,” said Kent Massey, the director of advanced programmes at HDT Global, a robotics firm based in Solon, Ohio. “It has been about speed. It’s been awesome, but a standard arm today is precise and stiff and heavy, and they’re really dangerous.” 

Massey’s company is one of a number of robot-arm designers that are beginning to build safer machines. Rethink Robotics in Boston and Universal Robots in Denmark have built “compliant” robots that sense human contact. The Universal system uses a combination of sensors in its joints and software, and the Rethink robot uses “series elastic actuators” — essentially springs in the joints that mimic the compliance of human muscles and tendons and acoustic sensors so the robot can slow when humans approach.

Beyond advances necessary for basic safety, scientists are focusing on more subtle aspects of touch. Last year, researchers at Georgia Tech reported in the journal Science that they had fabricated bundles of tiny transistors called taxels to measure changes in electrical charges that signal mechanical strain or pressure. The goal is to design touch-sensitive applications, including artificial skin for robots and other devices. 

Much research is focusing on vision and its role in touch. The newest da Vinci Xi, a surgery system developed by Intuitive Surgical Inc., uses high-resolution 3-D cameras to enable doctors to perform delicate operations remotely, manipulating tiny surgical instruments.

The company focused on giving surgeons better vision, because the necessary touch for operating on soft tissue like organs is still beyond the capability of haptics technology.

Curt Salisbury, a principal research engineer at SRI International, a nonprofit research institute, said that while surgeons could rely on visual cues provided by soft tissues to understand the forces exerted by their tools, there were times when vision alone would not suffice. 

Other researchers believe that advances in sensors that more accurately model human skin, as well as algorithms that fuse vision, haptics and kinematics, will lead to vast improvements in the next generation of robots.

One path is being pursued by  Eduardo Torres-Jara, an assistant professor of robotics at Worcester Polytechnic Institute in Massachusetts, who has defined an alternative theory he describes as “sensitive robotics.” He has created a model of robotic motion, grasping and manipulation that begins with simply knowing where the robot’s feet or hands meet the ground or an object. 

“It is all about recognising the tactile events and understanding that very well,” he said. Using biologically inspired artificial skin that can detect tiny changes in magnetic forces, he has built a two-legged walking robot that is able to balance and stride by measuring changing forces on the bottoms of its feet.

The students followed with new projects, tweaking the hardware and sharing programmes they had created. Dr Okamura said their enthusiasm was understandable.

“If you have all these senses — vision, hearing, taste, touch and smell — and someone took them away from you one by one, which is the last one you would give up?” she asked. “Almost everyone says vision, but for me, it would be touch.”