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Linear motor challenges materials-handling drives

03 May, 2011

SEW-Eurodrive has announced a modular synchronous linear motor system which can be used as an alternative to conventional drives in horizontal materials-handling applications. The SLC system can be assembled into lengths stretching hundreds of metres, and is said to reduce energy consumption by more than 60% in some applications.

Unlike conventional drive systems based on chains or friction rings, the linear motor has no mechanical wear, no contacts and produces little noise. It consists of a fixed primary containing windings, moving secondaries of various lengths incorporating ferrite permanent magnets, and an encoder box.

The low-cost ferrite magnets are arranged on a carrier plate, producing a long, narrow rotor. These magnets are not subject to the sourcing problems that are affecting rare-earth magnets and are rust-free, even at 100% humidity, thus avoiding the need to encapsulate them. OEMS can integrate the secondaries into structures such as the underfloor of materials-handling trolleys.

The motor’s primaries are powered by a frequency inverter from SEW’s Movidrive range. This evaluates the commutation information from a sensor box to ensure the correct current transfer from one winding to the next. It works in the coupling area between the trolleys, where no magnets are present. Typically, two to four primaries will be connected in parallel to an inverter.

SEW expects the linear motors to used mainly in distributing conveyors (sorters) in applications such as baggage-handling and mail order distribution centres. In these applications, dynamic properties are less important than energy efficiency.

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