Ultra-fast robot arm catches objects in mid-air

Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a robotic arm that can catch complex objects tossed to it—including a ball, a half-full bottle and a tennis racquet. Measuring 1.5 meters long, the arm uses its three joints and four-fingered gripper, along with a bank of cameras and a real-time control system, to dynamically calculate the trajectory of the object in mid-air and position the robot’s end effector in less than five hundredths of a second.

While catching a ball is impressive by itself, what sets EPFL’s robot apart, say its creators, is its ability to snag objects with handles offset from their center of gravity (tennis racquet/hammer) or with centers that dynamically change when thrown (half-full bottle).

“Today’s machines are often pre-programmed and cannot quickly assimilate data changes,” said Aude Billard, head of LASA. “Consequently, their only choice is to recalculate the trajectories, which requires too much time from them in situations in which every fraction of a second can be decisive.”

To teach the robot how to react quickly enough, the LASA researchers used a technique called programming by demonstration. Using this method, the programmers showed the robot examples of possible trajectories by manually guiding the arm to the projected target.

During this learning phase, objects are thrown several times in the robot’s direction, while a bank of cameras and high-speed controllers allow it to model the objects’ kinetics based on their trajectories, speeds and rotation. This model is then translated into an equation that allows the robot to quickly position itself whenever an object is thrown. During the few milliseconds of the approach, the machine refines and corrects the trajectory for a real-time and high precision capture.

According to the EPFL team, the arm is being developed for the Swiss Space Center potentially to clean up the growing amount of space debris. Since there’s no way to predict the trajectory of space junk, the EPFL robot arm, mounted on a satellite for example, would be tasked with dynamically grabbing the junk as it passed by.
www.epfl.ch