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12/06/2007
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Tom Shelley reports on state of the art in belt-driven actuators
Linear belt actuators are now setting new benchmarks in low cost, high speed and versatility.
In the low-cost arena, igus was showing its DryLin ZLW range at the recent Hanover Fair. This is a solution capable of positioning loads of up to 15kg. So, how is it different? Belt clamps and end pulleys are made of plastic, instead of aluminium, to reduce costs, while speeds are up to 2 m/s. The DryLin ZLW-06-30 weighs just 1kg and is 1m long. Like the rest of the range, the sliding elements are maintenance and lubrication free, being made out of the company’s proprietary ‘iglidur J’ polymer composition, while the bearings are ‘iglidur L250’. The drive belts are made of glass fibre reinforced Neoprene (the DuPont brand name for polychloroprene). The ZLW-06-30 is the result of enquiries from industries that include medical, packaging and food engineering, all of which had applications with confined installation space.
“We don’t believe there is a linear drive system that comes close to this, in terms of performance and price,” claims Matthew Aldridge, bearings product manager at igus UK.
The maximum speed of such systems appears to be 10m/s – as exemplified by the Festo DGE-ZR-RF range of belt-driven linear actuators with roller guides. Stroke lengths are up to 5m and maximum load of the largest size 63 is 60kg, although acceleration is then limited to 20 m/s2. The belts are made of nylon-coated polychloroprene, with glass cord reinforcement.
Schaeffler, meanwhile, sells triple-toothed belt drive tandem actuators, with a maximum rated speed of 3 m/s. At the fair, however, it unveiled a KUVE-B-HS four-row linear recirculating ball bearing and guideway assembly, also rated at 10 m/s. The company does not sell it as part of a belt-driven actuator as yet, although there was a demonstration on its stand in which it was belt-driven.
“Our competitors need special material, such as ceramic balls, to make these,” said Schaeffler’s Ralf Moseberg. “We use standard steel balls. We don’t go in a radius from the load zone to the recirculating area; we have a special curvature. We have around 4mm longer in the end piece, which is made of a proprietary blend of polymers. First applications are in semiconductor and printing industries, and we expect it to be used in high dynamics manufacturing, such as in PCB component insertion machines.”
The use of steel balls is claimed to give the new assembly enhanced load carrying capacity and a 30% improvement in service life.
Also novel – and available from two suppliers – are belt drive units with fixed centre drive units and profiles that move. In each case, the drive unit has a toothed drive pulley and two idler pulleys to ensure that the toothed belt engages the toothed drive pulley over at least 25% of its circumference.
Igus says its unit, designated a ZAW lightweight extension arm drive, is designed to extend into a working area even in highly dynamic applications. Festo’s catalogue contains a product designated the DGEA Boom Axis, whose construction looks remarkably similar – except that it has a recirculating ball bearing guide (the igus product has polymer bearings). Maximum stroke is 1m, maximum load is 20kg and maximum speed 3m/s. Applications for both products are seen in robotics, automation and mechanical handling.
Pointers
* Costs are coming down, at least for some products
* Maximum speeds are up to 10 m/s
* Variants are available, in which the drive units are fixed and the profiles, with their applied loads, move
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Author
Tom Shelley
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