New bellows grippers for handling fragile workpieces

Festo's DHEB bellows grippers are suitable for a diverse range of processing and manufacturing industries, spanning the food, pharmaceutical, general industrial and electrical sectors. Typical applications include general handling, sorting and packaging of fragile workpieces such as glasses, bottles, cups, beakers and ceramic containers. One major application is in the handling of PET (polyethylene terephthalate) bottles, which may be subjected to a variety of functions during the gripping process, including leak testing, disinfecting or filling.

DHEB grippers are single-acting devices, which simplifies their control significantly. When their air supply port is pressurised, an internal piston optionally draws a wedge up or down within a rubber bellow, causing it to deform outwards to meet and conform with the interior contour of the workpiece. This provides a secure but gentle and air-tight grip, which is maintained until the air supply port is exhausted, whereupon the force of the bellows returning to their original shape pushes the piston back into its initial position to release the workpiece.

Two versions

There are two versions of the DHEB gripper, offering a choice of bellows activation directions to suit different handling machine actions; one uses an upward piston stroke to deform and expand the bellows, while the other uses a downward stroke. Furthermore, the grippers are not limited to gripping the inside of workpieces: multiple units can be configured for grasping external surfaces, such as the edges of a printed circuit board or oddly-shaped profiles that would be difficult to handle using conventional grippers.

For maximum application flexibility, the compressed air supply for the gripper can either be applied via a side port on the body of the gripper, or via a connector at the top of the unit. Alternatively, a variant of the side-ported version provides a straight-through path from the top connector to a port on the underside of the piston. This can be used for a wide variety of purposes; air can be injected to cool or clean the workpiece, air or vacuum can be employed to check the workpiece for leaks, or fluid can be introduced for disinfection or filling purposes. Any of these actions can be performed during workpiece transportation, which helps users maximise machine throughput by overlapping or combining multiple process stages.

Sizes and load capacities

DHEB series grippers are available with 11 choices of contiguous bellow sizes, ranging from 8 to 63mm. The 8mm model is suitable for workpiece diameters from 8 to 11mm, while the largest gripper can accommodate workpiece diameters from 66 to 85mm. Depending on various factors such as friction and the shape of workpiece, the largest grippers can accommodate workpiece weights as high as 52kg. All models are designed for use with a standard supply of filtered compressed air, with a nominal operating pressure of 4 to 8bar. To reset the bellows to their unexpanded form, the pressure to the unit's air supply port simply needs to be reduced to 1bar or less. Opening and closing times depend on the size of the bellows; the 8mm model, for example, opens in 10ms and closes in 30ms.

Festo also offers a choice of bellows material to suit different applications. Silicone bellows have a very long service life - in the order of 1million cycles - and an extended operating temperature range of -70 to 200degC. The material is also approved by the FDA (USA Food and Drug Administration) for use in food processing applications. For applications demanding a higher coefficient of friction, such as internally gripping heavy straight-sided workpieces, or when the workpiece might subsequently be painted or coated, bellows manufactured from ethylene propylene synthetic rubber (EPDM) are available. These have a service life of about 0.5million cycles and a temperature range of -50 to 140degC. Both types can easily be replaced by the user, which helps to minimise maintenance time and costs.

Festo says that, uniquely, DHEB grippers can optionally be equipped with magnetoresistive or reed switches to sense the upper and lower positions of the internal piston, and provide control feedback on the state of the gripper bellows. The switches are self-aligning and mounted on an external sensor rail that is secured to the body of the unit.

Follow the link for more information about the Festo DHEB grippers. This website features animated presentations showing the action of the gripper's internal pneumatically-driven piston, and the manner in which the bellows deform.