In experiments, Digger Finger dug through granular media such as sand and rice, correctly sensing the shapes of items it encountered. The researchers said the robot might one day perform various subterranean duties, such as finding buried cables or disarming buried bombs.
The research will be presented at the next International Symposium on Experimental Robotics. The study's lead author is Radhen Patel, a postdoc in MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL). Co-authors include CSAIL PhD student Branden Romero, Harvard University PhD student Nancy Ouyang, and Edward Adelson, the John and Dorothy Wilson Professor of Vision Science in CSAIL and the Department of Brain and Cognitive Sciences.
Ground Penetrating Radar and ultrasound can be used to identify buried objects, but these techniques provide a hazy view of them.
"So, the idea is to make a finger that has a good sense of touch and can distinguish between the various things it's feeling," Adelson said in a statement. "That would be helpful if you're trying to find and disable buried bombs, for example."
In prior work, the researchers used a tactile sensor called GelSight that consisted of a clear gel covered with a reflective membrane that deformed when objects pressed against it. Behind the membrane were three coloured LED lights and a camera. The lights shone through the gel and onto the membrane, while the camera collected the membrane's pattern of reflection. Computer vision algorithms then extracted the 3D shape of the contact area where the soft finger touched the object. GelSight is said to have provided an excellent sense of artificial touch, but it was bulky.
For the Digger Finger, the researchers changed the shape to be a slender cylinder with a bevelled tip. Next, they removed two-thirds of the LED lights, using a combination of blue LEDs and coloured fluorescent paint. "That saved a lot of complexity and space," said Ouyang. "That's how we were able to get it into such a compact form." The final product featured a device whose tactile sensing membrane was about 2cm2.
The researchers then mounted the finger on a robot arm to dig through fine-grained sand and coarse-grained rice. Granular media can jam when numerous particles become locked in place so the team added vibration to the Digger Finger's capabilities and put it through tests.
"We wanted to see how mechanical vibrations aid in digging deeper and getting through jams," said Patel. "We ran the vibrating motor at different operating voltages, which changes the amplitude and frequency of the vibrations." They found that rapid vibrations helped "fluidise" the media, clearing jams and allowing for deeper burrowing.
According to Adelson, Digger Finger is part of a program extending the domains in which robotic touch can be used. "As we get better at artificial touch, we want to be able to use it in situations when you're surrounded by all kinds of distracting information," he said. "We want to be able to distinguish between the stuff that's important and the stuff that's not."