Soft-fingered gripper allows robots to manipulate cables

Even for humans it can be challenging to manipulate thin flexible objects like ropes, wires or cables, and therefore even more so for a robot. The problem is that as a cable slides between the fingers, its shape is constantly changing, and the robot’s fingers must be constantly sensing and adjusting the cable’s position and motion.

Now work at MIT’s Computer Science and Artificial Intelligence Lab (CSAIL) has shown that it is possible to build a robotic gripper that can be used for the fine manipulation of objects like cables and threads. The robot’s design is based on how humans use their fingers to do things like untangle wires and tie knots.

Past approaches have used a series of slow and incremental deformations, as well as mechanical fixtures, to get the job done, according to the researchers. CSAIL pursued the task from a different angle, in a manner that more closely mimics us humans. The team’s new system uses a pair of soft robotic grippers with high-resolution tactile sensors (and no added mechanical constraints) to successfully manipulate freely moving cables.

One could imagine using a system like this for both industrial and household tasks, to one day enable robots to help us with things like tying knots, wire shaping or even surgical suturing.

The team’s first step was to build a novel two-fingered gripper. The opposing fingers are lightweight and quick moving, allowing nimble, real-time adjustments of force and position. On the tips of the fingers are vision-based GelSight sensors, built from soft rubber with embedded cameras.

The team’s second step was to create a perception-and-control framework to allow cable manipulation. For perception, they used the GelSight sensors to estimate the pose of the cable between the fingers, and to measure the frictional forces as the cable slides. Two controllers run in parallel: one modulates grip strength, while the other adjusts the gripper pose to keep the cable within the gripper.

When mounted on the arm, the gripper could reliably follow a USB cable starting from a random grasp position. Then, in combination with a second gripper, the robot can move the cable ‘hand over hand’ (as a human would) in order to find the end of the cable. It could also adapt to cables of different materials and thicknesses.

As a further demo of its capabilities, the robot performed an action that humans routinely do when plugging earbuds into a mobile phone. Starting with a free-floating earbud cable, the robot was able to slide the cable between its fingers, stop when it felt the plug touch its fingers, adjust the plug’s pose and finally, insert the plug into the jack.

“Manipulating soft objects is so common in our daily lives, like cable manipulation, cloth folding and string knotting,” said Yu She, MIT postdoc and lead author on a new paper about the system. “In many cases, we would like to have robots help humans do this kind of work, especially when the tasks are repetitive, dull or unsafe.”

The algorithms the team developed can be generalised to different cables with various physical properties like material, stiffness, and diameter, and also to those at different speeds.

In the future, they plan to study more complex cable manipulation tasks such as cable routing and cable inserting through obstacles, and they want to eventually explore autonomous cable manipulation tasks in the auto industry.

Yu She wrote the paper alongside MIT PhD students Shaoxiong Wang, Siyuan Dong and Neha Sunil; Alberto Rodriguez, MIT associate professor of mechanical engineering; and Edward Adelson, the John and Dorothy Wilson Professor in the MIT Department of Brain and Cognitive Sciences.

Top image: MIT News