Adventures in collecting: Kenneth Salisbury's robot hand

By Carlene E. Stephens
A blue robotic arm

A visitor to Kenneth Salisbury's Stanford University office can't miss the evidence of his life-long fascination with hands.

Ken Salisbury sits in his office smiling. In the foreground is a pink translucent model of a human hand. He sits behind it at his computer.
Kenneth Salisbury in his office at Stanford University. Salisbury is Professor Emeritus in the departments of Computer Science and Surgery-Anatomy.

On every horizontal surface there are robot fingers, joysticks, touch-based instruments. There's even a human hand rendered in bright red resin, looking a lot like the Addams Family relative Thing. Salisbury recalls that as a kid he was always playing with something in his hands—trying out magic tricks, tying knots, playing musical instruments. He even built a robot finger when he was six years old. Later, he was inspired to help his father, a stroke victim, regain the use of his hand. It's not entirely surprising, then, that he designed and built a robot hand for his PhD project in mechanical engineering at Stanford in 1982, formed a company to manufacture them for select customers, and stuck with the subject for the rest of his career.

C-3PO a shiny, golden humanoid robot stands with his arm closest to the lens of the camera.
This is not the robot you're looking for. C-3PO, based on art by Ralph McQuarrie, appears in the Star Wars films. For many, the robots that appear in science fiction are more familiar than actual robots.

Does a robot hand conjure images of C-3PO's golden fingers? Or the Terminator's silvery endoskeleton digits? These movie props, fashioned after human hands, are more familiar than those of actual robots emerging from industrial and academic labs. According to engineers working in robotics today, designing a robot hand that functions almost like a human's is one of the most difficult research problems they face.

That's because the human hand is a wonder of dexterity. The exquisite complexity and sensitivity of our hands, in concert with our brain, enable us to perform an extraordinary range of tasks in different situations—to wield a screwdriver, say, or stroke a puppy. Not so with robotic imitations. Before Salisbury's invention, at the end of robot arms were tools called "end-effectors," not even close to looking or working like a human hand. They had difficulty interacting with objects of differing shapes, sizes, and materials. Even today, practical versions of robot hands are still at their best when doing one well-defined task repeatedly, like assembling a computer chip or spot welding a car body. But with the advent of Salisbury's invention, robot hands began to approach the skill level of human hands. 

Picture a blue mechanical caterpillar. This robot hand sort of looks like that with an "arm" showing its mechanisms, and fingers with orange finger tips.
The museum recently acquired this Salisbury robot hand. 

We've just added one of Kenneth Salisbury's fascinating robot hands from the 1980s to the museum's robot collections, a century-spanning group of objects that documents historical robots and other automatic machinery in industry, research, and entertainment. An intriguing piece of machinery, the Salisbury hand has three identical fingers, each of which has three joints. To actuate the hand, a total of a dozen tension cables are pulled upon by an equal number of electric motors. The motors move the fingers with controlled forces and motions. Sensors in the base of each robot finger permit control of the tendon tensions and finger forces, enabling the fingertips to grip and manipulate objects of varying sizes and shapes. In the early 1980s, this design provided a whole new way to coordinate three fingers so that the robot hand could not only grasp objects but also simultaneously move them within the grasp. For example, this ability enabled the hand to grasp a shaft and fit it into a hole by pushing and wiggling until the hand detected that the shaft was fully inserted. The action is analogous to what a human does when assembling objects. This improvement in machine-grasping versatility served as the foundation for future efforts to devise defter robot hands.

A human-scale programmable robot arm typically supported the hand and moved it through its workspace, and both were controlled by a computer. Devising a robot arm was a feat in its own right, the brainchild of Vic Scheinman, another Stanford mechanical engineering PhD student, who preceded Salisbury by about a decade. (The museum also has a prototype of Scheinman's invention, developed with Unimation and General Motors and known as the PUMA, or Programmable Universal Machine for Assembly.) 

The museum's robot hand is one of about 20 made in the 1980s at Salisbury Robotics Inc., a manufacturing firm Salisbury set up in Palo Alto, California. Sandia National Laboratories in Albuquerque, New Mexico, acquired this robot hand in 1984 to experiment with its potential for handling hazardous materials and working in hazardous places, among other things. Sandia researcher Cliff Loucks remembers the machine had a "sweet" design and a hefty price tag—$32,265.00.

NASA also provided funds for refining the hand, a potential tool for the space station and other applications. Although some industrial firms had secret robot experiments underway at the time, there was no other commercially available robot hand except Salisbury's.

Salisbury continued to work on machine-based hands and touch-related projects after success with the robot hand. At the Massachusetts Institute of Technology, in the Mechanical Engineering Department and Artificial Intelligence Lab, he and his students developed more useful machines. One, with student William Townsend, was a robot arm now in worldwide use known as the Barrett WAM arm (WAM is Whole Arm Manipulation). Another was the first remote-controlled surgical robot called the Black Falcon and still another enabled users to literally feel virtual objects by use of the haptic (or touch) interface they developed. Salisbury moved on to Intuitive Surgical, where he continued investigations in enhancing the surgeon's skills with robots and contributed to the da Vinci Surgical System. (The museum has a da Vinci surgical robot on display in Many Voices One Nation.) He then returned to Stanford and focused his research on medical robotics, surgical simulation, and designing robots for interaction with humans.

Kenneth Salisbury demonstrates something using a robot and his fingertip in his office.
Kenneth Salisbury, in his office at Stanford University, demonstrates a PHANToM haptic interface, an instrument he and student Thomas Massie designed at MIT to enable feeling virtual objects. 

In that office full of robot parts, it's easy to picture Salisbury inspiring a steady stream of brilliant students and advising on their projects. With his open-handed warmth and generosity, he's a natural teacher. He continues to follow his passion for investigating robotics, human-machine interfaces, wearable robotics, and, of course, hands.

Carlene Stephens is a curator in the Division of Work and Industry. She has also blogged about Stanley, a self-driving car.

The Salisbury hand is part of the National Museum of American History's collection of robots and other automatic machinery from industry, research, fantasy, and entertainment. Highlights of the collection include self-driving vehicles from the DARPA Grand Challenges (2005), a Unimate industrial robot (1961), a photosensitive "tortoise" designed by brain researcher W. Grey Walter (1952), R2-D2 and C-3PO costumes from Return of the Jedi (1983), a talking doll from Thomas Edison's phonographic works (1890), and a Renaissance automaton of a friar that walks and prays (1560). You can see the Salisbury hand in action.