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Bi-parting drive helps with conveyor centring
Published:  08 April, 2011

Festo has announced a novel electric drive that provides a cost-effective, adaptable means of moving two carriages simultaneously in opposite directions on the same linear axis. Typical applications for the ELGG bi-parting drive include centring items on conveyor systems, opening and closing safety doors on machinery, and driving large-format gripping equipment.

The drive has a pair of bearing guides supporting two identical carriages, driven by a toothed belt attached to the top of one carriage and the bottom of the other. This arrangement causes the carriages to move simultaneously, either away from, or towards, the centre line of the axis.

The drive (shown above) dispenses with the full-length profile used by conventional toothed belt axes, relying instead on the rigidity of steel bearing guides to ensure that the carriages move in straight lines. The bearing guides are supported at either end, with the option of a centre support, resulting in a rigid, robust structure. The supports and the carriages are made from the same extruded aluminium profile to cut costs, and use an asymmetric extrusion geometry to provide the necessary offset.

The drives are available in 35, 45 or 55mm-wide profiles, with maximum standard stroke lengths, per carriage, of 400, 500 and 750mm, and maximum total feed forces of 50, 100 and 350N, respectively. Longer stroke lengths are available to special order.

The moving carriages can be equipped with sliding bushings or with recirculating ball bearing guides for higher speeds and loads. Depending on configuration, the drives are capable of speeds up to 3m/s, and can provide repeatable positioning accuracies to within ±100 microns. Service lives are claimed to be more than 5,000km of travel.

The feed force available from bi-parting drives is averaged between the two carriages. This means that if one carriage is subject to zero load – for example, when centring an item on a conveyor system – the other carriage can provide the full feed force.

The bi-parting drives offer various configuration options and accessories. Both sides of the axis can be equipped with a second standard-length or extended-length carriage to accommodate loads with relatively high twisting or turning moments. Festo is also offering a passive guiding axis variant (known as the ELFR)  which dispenses with the belt or pinions and can be used alongside an ELGG drive to improve rigidity and resistance to torsional loads.

End-position sensing is provided by flush-fitting inductive sensors which sit in slots in the centre and end supports of the axis, and detect the presence of flag plates on the moving carriages. Each sensor has a clearly visible LED status indicator for ease of adjustment during commissioning.

The bi-parting drives are compatible with Festo stepper and servo motors and controllers, and can also be used with third-party motors. The motor can be mounted at either end and on either side of the axis. Installation is simplified by a hollow drive pinion and an elastomer motor coupling with an expanding shaft, which provides a highly reliable, backlash-free connection.

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