Researchers at MIT and Northeastern University have equipped a robot called Baxter with a novel tactile sensor that lets it grasp a USB cable draped over a hook and plug it into a USB port. According to Robert Platt, an assistant professor of computer science at Northeastern, for a robot taking its bearings as it goes, this type of fine-grained manipulation is unprecedented. The sensor is adapted from a 2009 MIT technology called GelSight. The new GelSight sensor isn’t as sensitive as the original but it’s smaller - small enough to fit on a robot’s gripper - and its processing algorithm is faster, so it can give the robot feedback in real time. The sensor is a plastic cube with a layer of transparent, synthetic rubber coated on one side with a metallic paint. The four walls of the cube adjacent to the sensor face are translucent, and each conducts a different color of light - red, green, blue, or white - emitted by LEDs at the opposite end of the cube. When the gel is deformed, light bounces off of the metallic paint and is captured by a camera mounted on the same cube face as the diodes. From the different intensities of the different-colored light, the algorithms developed by team can infer the three-dimensional structure of ridges or depressions of the surface against which the sensor is pressed.