Bernoulli effect: gripping with overpressure

Article of 24 May 2013 

The Bernoulli effect in automation

It’s been known for more than 250 years but the Bernoulli effect is just as fascinating as ever – an elementary effect in fluid dynamics resulting from flowing gases and liquids. It was discovered by Swiss mathematician and physicist Daniel Bernoulli. Stated simply, a partial vacuum results when a medium, for example air, flows passed an object quickly. The object is not blown away, as one would expect, but rather sucked in.

Aeroplanes make use of this surprising effect – it provides them with the lift they need in order to fly. And motorcyclists are familiar with it as well: when quickly passing a truck, air flows at high speed between the motorcyclist’s body and the truck shell. A partial vacuum results which draws the motorcyclist towards the truck. The Bernoulli effect can be demonstrated with a simple experiment: hold two broad strips of paper at a distance of roughly ten centimetres from each other in front of your mouth and blow down forcefully between them, and they are drawn together. This is due to the partial vacuum generated by the air flowing between the sheets.

The Bernoulli effect in automation

This effect is made use of in automation technology, for example in Bernoulli grippers. This method is especially well suited for handling sensitive objects such as silicon wafers – very thin semiconductor wafers which are required for the production of solar cells. The workpieces are retained by applying overpressure to the gripper. Although air is blown towards the workpiece, it’s drawn in thanks to the Bernoulli effect and an extremely small gap is maintained between the workpiece and the gripper as well. Even objects with porous or irregular surfaces can be retained in this way, which would not be possible with a vacuum gripper. This contactless handling technique also prevents permanent deformation of the workpiece.

Festo Bernoulli gripper

Festo Bernoulli gripper

Festo has further developed existing Bernoulli gripper technology and now achieves four times the retaining force of similar grippers from other manufacturers thanks to a flow-optimised design, and by taking better advantage of available surface area. Noise has also been minimised: the developers have prevented the generation of large, noise-causing air eddies in the gripper with the help of an improved layout. The photovoltaic industry has thus far been a primary user of these grippers. But product developers at Festo also see potential in the handling of carbon fibre mats, carpets and assembled PCBs.