Picking a winner
April 1st 2009

Highly automated goods-to-man systems ensure picking personnel are kept busy and supplied with a constant flow of goods. In this way an efficient automated storage & retrieval system (AS/RS) can be installed to bring a faster return on investment, claims Andy Smith, managing director of TGW

Goods need to be transported in suitable load carriers for both efficient handling within an automated warehouse and for highly automated picking. Shape tolerance, sag, easy running qualities and suitability for stacking are all important load carrier criteria.

Ensuring that the right goods are delivered to the picking workstation at the right time and in the right quantity, is key to any high performance goods-to-man system, particularly automated small parts warehouses where enormous strides have been made in performance over the past 6 years.

As racking structures get higher, they need high performance devices to allow the volume offered by such a large storage position capacity to be utilised efficiently.

Single mast devices, such as TGW's Mustang, can already achieve over 150 double-actions per hour, thanks to high travel rates from an acceleration of up to 4 m/sÇ and maximum speed of 6 m/s. Twinmast devices, while slightly less dynamic due to their larger structure, can also achieve high performances by using several load handling devices. In fact even higher performances can be achieved than for the single master with up to 200 double-actions possible when the load handling devices travel uncoupled from each other and vertically on both masts, as is the case with TGW's Stratus D.

200 double-actions and more When performance is the focus, lower height applications are more suitable, such as TGW's Booster stacker crane or using stacker cranes within a lift beam construction like the TGW-Commissioner.

The Booster achieves 250 storage/retrievals in 'double-play' - using its two load handling devices - at a maximum height of 5 m with an acceleration of 5 m/sÇ and a top speed of 5 m/s. TGW's slender yet tall Commissioner achieves similar rates.

High performance conveyor systems Further down the line, conveyor system performance will influence workstation supply. Reliable high-performance modules such as TGW's Multi Roller Conveyor, provide fast, yet careful transport. Device flexibility is particularly important for pressure-free accumulation buffer functions, which can be actuated either purely mechanically or electromagnetically.

Special attention must be paid to transfer and sorting functions – there's a significant difference in performance between a cumbersome turn-and-lift device and a highly dynamic pop-up shift. Shoe sorters or high performance pop-up sorters achieve performances of over 10,000 units per hour, which makes them a favoured solution in mail-order dispatch sorting.

Decentralised buffers are another important element in dynamic picking systems for sequencing workstation supply, smoothing out load peaks and for revolving sorting cycles. Potential variants range from a parallel arrangement of several accumulation conveyor lines through to tower storage and Commissioner solutions down to highly dynamic Booster warehouse applications.

High-performance workstations Ergonomic workstations are another major component in achieving high-performance in picking. Diagonal positioning of the totes is a good example of how to improve the view offered of the contents while making the goods easier to reach. Size and weight of the goods also need to be taken into account in the way they are arranged.

Pick-by-light and pick-to-light show what movements are to be made without the employee having to first search for the goods to be picked, while the quantity is provided on a display.

Automated picking While highly automated picking systems are linked to relatively high investment costs this needs to be balanced against the enormous advantages line operators can reap.

An 8 to 10 times increase in picking performance compared to simple man-togoods systems is the first point to consider.

Every picker's working performance is optimised through a permanent supply of goods for picking, while the amount of tiresome walking is reduced; workstations designed around Designing workstations around ergonomic principles can also provide an immense performance advantage.

Another plus is a major increase in picking quality. Precise guidance of pickers ensures errors are avoided, while additional controlling functions such as a weighing system adds further reliability. Lower error rates bring immediate benefit in terms of a drastic reduction of work involved in dealing with returns and delivery corrections.

Simultaneously, customers service levels are increased.

Finding large numbers of qualified employees for picking can be hard, while staff turnover can often be too high to ever achieve satisfactory quality and performance. Seen overall, the economies generated by automated picking systems can frequently lead to a return on investment in only one to three years.

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