Wrist-Mounted Robot Adds Extra Fingers

Massachusetts Institute of Technology, Cambridge, MA

Human thumbs are amazing things, adding abilities for grasping that most other mammals don’t have. Now, mechanical engineers at MIT have developed a robot that enhances the grasping motion of the human hand.

Faye Wu, a graduate student in mechanical engineering, demonstrates the “supernumerary robotic fingers” device. (Credit: Melanie Gonick)

The device, worn around the wrist, works like two extra fingers adjacent to the pinky and thumb. Its novel control algorithm allows it to move in sync with the wearer’s fingers to grasp objects of various shapes and sizes, and provides an intuitive and natural way to move the robotic fingers to assist natural fingers, they said.

The two-fingered robot may be used to assist people with limited dexterity in performing routine household tasks, such as opening jars and lifting heavy objects. The robot, which the researchers have dubbed “supernumerary robotic fingers,” consists of actuators linked together to exert forces as strong as those of human fingers during a grasping motion. (See Figure 1)

To develop an algorithm to coordinate the robotic fingers with a human hand, they first looked to the physiology of hand gestures, realizing that only two general patterns of motion are used to grasp objects: bringing the fingers together, and twisting them inwards.

They then hypothesized that a similar biomechanical synergy could be used for seven fingers, instead of just five. To test this hypothesis, a researcher wore a specialized glove fitted with multiple position-recording sensors attached to her wrist via a light brace, and grasped a variety of objects, manually positioning the robotic fingers to support the object. She then recorded both hand and robotic joint angles multiple times with various objects.

The researchers then analyzed the data, and found that every grasp could be explained by a combination of two or three general patterns among all seven fingers. They used this information to develop a control algorithm to correlate the postures of the two robotic fingers with those of the five human fingers, essentially teaching the robot to assume a certain posture that the human expects the robot to take.

For now, the robot mimics the grasping of a hand, closing in and spreading apart in response to a human’s fingers. Their next step is to teach the robot to use different amounts of force for various objects, and eventually, to account for personal grasping preferences.

While just a prototype for now, the researchers hope to scale down the robot to a less bulky form, about one-third of its current size, and make it foldable, so that the fingers can pop up to be used when needed, and away when not.

To see a video of the device in action, go to www.techbriefs.com/tv/robotic-fingers.