Human dexterity allows for seemingly simple tasks like picking up objects and adjusting the fingers to achieve the right grip. Behind it is an intricate system that includes 26 bones, muscles, skin and, of course, instant direction from the brain. How human dexterity truly works to perform tasks like picking up a pen is still somewhat of a mystery.
“You move the pen from an initial grasp to something more stable, but to do that, you’re gripping it with certain surfaces of the fingers and sliding it against other surfaces of the fingers,” said Adam Spiers, a former associate research scientist at Yale University. “It’s really quite complicated as far as all the force and frictional interactions go, but we all take it for granted as a very simple thing to do.”
Creating a robot that can mimic those actions may seem like an impossible task. Although pick-and-place robots have progressed considerably, any that come close to completing complex human tasks are typically not priced affordably. As a member of the research team at Yale’s Grasping & Manipulation, Rehabilitation Robotics, and Biomechanics (GRAB) Lab, Spiers has made strides in bringing that reality one step closer.
The researchers developed Variable Friction robot fingers, a conventional gripper that can complete in-hand manipulation at a significantly lower cost. The somewhat simple design consists of two surfaces—a soft urethane (high-surface friction) and a hard 3D-printed plastic (low-surface friction)—that are suspended behind one another using rubber bands. The “fingers” form a robotic hand that include electrically moved pivot joints that can be manipulated in several ways.
“I think one of the key features of human hands that’s often overlooked is the surface properties of our fingers and what that allows us to do as far as moving objects within the hand,” Spiers said. “For example, when you make a light touch with your finger pads, they are able to slide over objects, while using a bit more force deforms the soft internal tissue and causes them to grip.”
Friction is the key to the robot fingers’ design. The urethane acts like a finger pad when a low-grip force is applied. It then switches to the hard surface, created from acrylonitrile butadiene styrene (ABS), at higher forces. This allows the robot hand to alternate between gripping and sliding, allowing for a range of manipulation options.
While the team’s design suggests what might be possible, it hasn’t quite achieved more subtle tasks that a human can perform. The team has made its research available so that others can potentially expand upon it and bring the abilities of robotic hands even closer to those of humans.
Interested in more robotic innovations? Check out Bipedal Robot Masters Balancing Like a Human and Research Team Develops Humanoid Construction Robot.