Product category:
Automated handling systems, AGVs, integrated handling systems
News Release from: ITS (UK) | Subject: Tote transport system
Edited by the Manufacturingtalk Editorial
Team on 09 April 2002
Tote transport system beats narrow aisle
cranes
A tote transport system helps a logistics operation achieve greater picking throughputs at a centralised warehouse than was previously possible with narrow aisle cranes.
A tote transport system from ITS (UK) helps Christian Salvesen's Neasden RDC achieve greater picking throughputs than was previously possible with narrow aisle cranes The investment also underlines the impact changing throughputs can have on major handling hardware investments
This article was originally published on Manufacturingtalk on 17 May 2001 at 8.00am (UK)
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One of three Christian Salvesen RDCs dedicated to Marks and Spencer, the Neasden centre distributes mainly textiles to 29 M and S stores throughout the southeast of England just in time.
Deliveries received on one day are despatched the next, and in some cases on the same day when cross-docked.
Unlike many retail operators, M and S do not move goods to stores in retail packs but expects its 3PL partners like Christian Salvesen to single pick everything.
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Inevitably, that has major implications for picking arrangements and the kind of hardware investment needed to support them.
Neasden found that its current picking throughputs for boxed items based on 35 manually-driven, narrow aisle cranes was throughput limiting when coping with changing business levels.
Confined to one aisle, each crane typically covered 3,200 storage slots and did not double cycle, ie put goods away and then pick for the return journey.
To raise throughput, therefore, the decision was made to remove nine crane aisles and convert them to mezzanine walkways on four floors.
The big advantage of walkway picking over fixed narrow aisle cranes, explained Christian Salvesen's site manager, Romas Kusneraitis, is the flexibility that labour affords for much higher throughput rates.
Feeding the four floors with tote-loaded dollies, however, depended on using three industrial lifts which posed bottleneck problems owing to the change in picking methods.
A new transit system, therefore, had to be found for moving stock among the four floors.
Seven major companies tendered and were briefed on the need for saving space and the kind of hourly throughput rates looked for.
The proposed solutions involved various types of conveyors and even paternosters but the ITS overhead conveyor system, combined with one elevator, proved the best solution in terms of its compact design and ease of expansion and automation upgrades.
Some of the other conveyor solutions "took up a lot more space then we thought was appropriate," explained Romas.
ITS is no stranger to Christian Salvesen, having installed its hanging garment overhead conveyors on the site when it opened 14 years ago and which are still working well today.
These conveyors use the rotating tube principle, rather than the more common chain driven types, which are more power and maintenance hungry, messy, and have a short life span generally no more then 10 years.
But the Salvesen investment does mark a first in Europe by using the new, twin track OCS system designed specially to take heavier loads up to 500 kg per conveyor trolley.
In Salvesen's case, the load-carrying capacity is 450 kg per trolley, including the heavy duty steel cages.
These suspended cages can take two roll cages, or 16 totes stacked on four dollies.
On each floor level, close by the elevator, there is a controlled accumulation buffer (CAB) five metre long for taking four suspended cage trolleys.
The reason for these buffers is that they do not have to be constantly manned.
About 40% of incoming flat pack items now arrive in tote boxes, thus greatly reducing waste handling problems associated with cardboard boxes.
The remaining 60% comes in cardboard boxes or loose plastic packaging which must then be placed in totes.
These goods are mainly textile items, home furnishings, soaps and perfumes, which when added to all other items stored elsewhere by the stacker cranes and hanging garment conveyors, account for between 70,000 and 80,000 SKUs.
All incoming loads are sent on belt conveyors to the first floor for scanning and labelling by one of 10 terminals.
Empty totes required for the intake terminals on the first floor are sent up on dollies by the three industrial lifts and stored next to the labellers.
Once labelled, the goods proceed to their storage slots spread across 35 crane aisles, including the nine converted to walkways.
There is, however, the facility to scan loads for the fast track area or cross docking, and thus by pass the walkway and crane storage areas.
Full tote boxes on dollies must still be manually pushed on each floor to cage trolley accumulation buffers.
Here, an operator collects an empty trolley cage and pushes it manually around the gravity curve into the loading area.
Via a ramp, the operator then pushes his stacked totes into the cage trolley, closes the door, and pushes the trolley away from the loading position to enter a step feeder just before the drive section.
Trolleys then move automatically on to the driven line and accumulate before the elevator.
By using a simple peg system on each trolley, the operator can direct the trolley to the appropriate floor.
On the infeed side, order pickers then take the dollied totes and decant the items into plastic trays housed in the aisle zones for which they are responsible.
Those same dollied totes are used to pick into the feed to the cage trolleys for removal via the single elevator to the despatch floor.
All putaway and picking instructions are under radio data terminal (RDT) control, so there is constant, real time stock control with very few picking errors.
If a trolley is addressed for a specific level and the buffer on that level is full, an alarm will sound on the floor and the information on the alarm read on the second-floor operator panel.
Working round the clock, the ITS tote transport system went live in May 2001.
It uses 29 cage trolleys and can deliver 1,800 totes an hour or 18,000 to 36,000 single items/hr given that each tote can take 10 to 20 items.
Citing the main benefits of the ITS investments, Romas explained "We now have a system that can get high volume downstairs as quickly as possible.
It takes up very little space and that is important to us.
If we had stayed with the cranes we would have had a problem with throughput." Keith Turnbull, ITS's engineer responsible for selling the tote transport concept, also added that the system does not result in any extra work.
"Once you have got your totes together, you load then into the machine and it takes them away.
If a flatbed conveyor had been chosen, you would have had to split the load and then consolidate them in order form as well.".
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