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Pressed for time? These trouser storage drives are a prefect fit

28 February 2012

We review a newly installed, automated storage and retrieval system based on Lenze frequency inverters and geared motors that is capable of handling a stock of six hundred thousand pairs of trousers at the rate of five thousand pairs per hour

Handling of materials for the consumer market demands efficient, low cost and reliable logistics. Add in e-commerce with the need to respond rapidly to small orders and a dedicated automation system becomes the key to competing successfully. German logistics specialist Durkopp has recently commissioned a highly automated storage facility that is capable of picking from a stock of 600,000 pairs of trousers at the rate of 5,000 pairs per hour.

The company specialises in the sorting and transport of flat and hanging goods such as clothing and they are market leaders, with many blue-chip customers worldwide such as M&S, Next, Asda, John Lewis and Zara.

Durkopp’s automation partner in this E7 million warehouse extension - Lenze - supplied geared motors and drives to meet the optimum material flow specifications. In addition, the new motor technology and control software in the Lenze 8400 series inverters that were chosen for this project have combined to deliver significant energy savings.

Roller adapter
The task was to automatically locate trousers from the stock without fixed storage locations, and to remove them in an order picking process at the specified rate. A development of Durkopp’s existing ‘roller adapter’ technology, where the garments are suspended from motorised overhead tracks, was used. For this installation hanging adapters were introduced with reduced dimensions and the ability to accept different types of hangers. The adapters are equipped with high reliability RFID tags for identification purposes and these provide excellent visibility to the control system so that position and quantity information is available continuously.

Only a small amount of power is required to move the ball bearing mounted rollers of the adapters – a big improvement on conventional systems based on high friction glide rails that has enabled the logistics specialist to make significant reductions in energy consumption. The power required for each drive module is now just 300W.

The installation has 32 storage units on each of three levels, and each storage unit can hold up to 7,000 pairs of trousers. With drive and buffering requirements, there are some 288 axes of geared motors and drives. The chosen hardware included Lenze’s 8400 StateLine frequency inverters and type GKR bevel geared motors, the latter being compact right-angle units offering an efficiency of 96%.

The StateLine inverters are installed in groups of 16 in control panels distributed through the warehouse. A CANopen system bus, which is built into these drives as a standard feature, is used for communication between the inverters, while communication with the higher level controlling PLC is achieved via EtherCAT. 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.

Energy saving software
Another useful feature provided by these drives is the plug-in memory chip that allows a drive to be exchanged and re-parameterised in just a couple of minutes. They are also able to run new energy saving software called VFCeco. Standard on the 8400 StateLine, HighLine and TopLine models, this function reduces the magnetising current in asynchronous motors.

When 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 and the magnetising current is reduced accordingly; as much as 30% reduction is possible. For Durkopp’s facility, where the number of roller adapters in each storage unit varies, and therefore the drive loads vary, the savings are significant.

Online purchasing dictated the high capacity of the new system, the average single order quantity in web shops being 2.7 items. The target of 5,000 items per hour is achieved by intelligent automation of the order picking process and subsequent correct sequencing using three-stage matrix sorters. Here, too, Lenze drives are used, but in a different configuration.

Decentralised drives
The spatial distribution of the drives is greater here, so the Lenze ‘drive package’ proved the best option. Each package comprises a three-phase motor, a bevel gearbox and a Series 8400 motec frequency inverter, which is mounted in the motor terminal box position (thus no panel space is required for the inverters). Power supply cables do not require screening and can be looped-through from inverter to inverter, saving a substantial sum in installation costs. The motec inverters are also capable of running the VFC eco energy saving software.

Motors for the matrix sorters are not standard three phase units but are instead drawn from the new Lenze MF range, which is designed for use with frequency inverters at an operating point of 120Hz. The benefit of the higher rated speed is that more power is obtained from a particular frame size. For example, a MF motor with IEC 71 frame size is rated at 1.5kW. A conventional three-phase motor requires a frame size 90 for this. The smaller frame size represents a reduced space requirement, lower purchase cost and reduced inertia - which in turn contributes to energy saving when there is frequent stopping and starting. According to Lenze, the running efficiency of its MF motors is well above IE2 levels.


Lenze’s drive package at-a-glance
The GKR bevel geared motor range is available in power capacities from 60W to 7.5kW, with output speeds from 14 to 1,000rpm. The 8400 StateLine frequency inverter range is available from 0.25 to 45kW, and it forms part of Lenze’s scaled 8400 range, which includes both positioning and servo motion functionality. The MF motor range, designed to operate at a frequency of 120Hz, comes in powers from 0.55 to 22kW, and frame sizes 63 to 132. The Series 8400 motec decentralised frequency inverters for wall or terminal box mounting are available across the power range 0.37 to 7.5kW.

 


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