Drive Technology for automated warehouses

The new warehouse installation has 32 storage units on each of three levels. With drive and buffering requirements, there is a total of 288 axes of geared motors and drives. Lenze type GKR bevel geared motors that run with a high efficiency of 96% were chosen in keeping with the end-user's requirements of minimising energy costs. These gearboxes are two stage with a shallow-ratio helical stage and a bevel output stage that gives ratios up to i=76 with a constant efficiency of 96%. Furthermore, wear in the gears is very low allowing a long maintenance-free life. The GKR range is available in four sizes suiting motor powers from 60W to 7.5kW.

Lenze inverters of the type 8400 StateLine were selected based on low installation and running costs. The StateLine inverters are installed in groups of 16 in control panels distributed through the warehouse. Communication is achieved in an easy, elegant and cost-efficient way. A CANopen system bus, which is built in as a standard without extra cost, is used for communication between the inverters. To communicate to the higher-level controlling PLC, EtherCAT is the preferred medium. A single EtherCAT communications module is all that is required for each group of 16 inverters. The frequency inverters deliver smooth and jerk-free starting and stopping. Another important feature is the pluggable memory chip that allows a drive to be exchanged and re-parameterised in a couple of minutes.

A final factor that was key to the end-user is the incorporation of new energy saving software called VFC eco. This function reduces the magnetising current in asynchronous motors. Particularly where three phase motors are partially loaded, the magnetising current will be higher than the actual conditions require. With the VFCeco software, the motor load is sensed automatically and the magnetising current is reduced to match. The result is savings of up to 30% in the current. In cases such as this warehouse, where loads in each storage unit vary, the savings are significant.

This application illustrates the importance of drive efficiency and lifetime running costs for the buying decision made by the end customer. Of course, performance is also important, but award of the contract was primarily based on running costs. These costs can be predicted in Lenze software DSD Drive Solution Designer, available on request for free trial.

For further details about Lenze geared motors and frequency inverters go to www.lenze.com.