Robo-Air Jet System makes small objects “levitate”

You might have tried to balance a ping-pong ball floating above your mouth or you might have seen a demo in a classroom or science museum where a jet of compressed air keeps a ball floating above the ground, seemingly defying gravity. A pair of grad students at the University of Illinois at Urbana-Champaign have taken the trick to the next level.They used a more powerful jet of air and an multi-axis robotic nozzle, in order to manipulate objects in three dimensions through obstacle courses, toss things, hold up multiple objects, weigh objects, and even peel onions.

Aaron Becker and Robert Sandheinrich, with help from professor Timothy Bretl, built a computer-controlled air jet system that can make spherical objects like ping-pong balls not only float in place but also move along complex trajectories or- even performing some acrobatic maneuvers like passing through wire loops. Their robotic air blower can also sort balls of different weights and precisely propel balls toward a target. And it can lift an apple and non-spherical objects like a water bottle.

The system consists of an air jet with two degrees of freedom. The air jet is supplied up to 620 kPa through a DC motor-controlled valve. Stereo vision cameras track the objects, and a control algorithm uses the position data and a fluid dynamics model to adjust the air jet, varying its speed and direction to keep the object in equilibrium.

Making a plastic ball “levitate” using compressed air is an old trick (the fast moving air creates a low pressure zone around the ball that traps it), but the UIUC guys had to solve a number of hurdles in engineering their system. The design of the control system, in particular, was a big challenge because the dynamics of the air flow can exhibit chaotic behavior, which is hard to model, and also because adding more than one ball changes the flow field in complex ways. Still, the system can manipulate spheres of various sizes (12 to 97mm in radius and 2.6 to 188g in mass).

The students, who presented their work at this year’s IEEE/RSJ International Conference on Intelligent Robots and Systems (full paper PDF), say that non-contact manipulation with an air jet could be used in applications that involve sorting small parts or handling flexible, delicate objects such as clothes, paper, and sliced fruit.