2018-01 Siemens Congleton
We were required to design and build a shelf trolley system that is to be towed by a pedestrian tug around the factory. This will be with the aim to distribute parts where required and sent offsite to their 3pl partner for restocking before returning.
Initially it was requested that a system be designed to allow 4 shelf trolleys of platform size 800 x 600mm to be towed as a train. However, with the 5 linkages that this would have required, the trolley would not be able to make the tight turns that is required as shown in the images below.
It was decided that a 2-trolley system of base dimensions 1600 x 600mm was a far more practical solution. This was still questionable given that a train including the tug and operator would be 5500mm long and they need to make 90 degree turns within aisles only 1185mm wide with the train following perfectly in order to make the turns.
It was also a requirement that the trolley could be towed to a location, the tug disconnected and reattached at the other end and towed back the other direction which meant that the trolley had to behave the same if towed from either end of the train. This meant that the pivot point of the connecting sections had to be located exactly at the midpoint between the trolleys and that the trolleys mirrored exactly.
There was one last requirement for this trolley system. Given that the trolleys had to be transported to and from site with product on, it was also required that there be a removable containment system which would add nothing to the overall dimensions of the product when removed.
Having come up with a concept that we believed could possibly work, we needed to prove or disprove the concept, so we mocked up 2 trolley bases to the correct dimensions. Siemens also sent us a tug so we could trial and tweak the design as required at an agreed prototype stage. We ensured there was one cost to include site trials if successful.
We laid out pallets in our yard to mirror the tightest turn and put the trolley through multiple tests. To our amazement it went around on the second go! We videoed it and you can find the video on our Facebook page. Please use the link below to view it for yourself!
We took the samples to site for trial and as we were assembling the system, everyone believed there was no chance of towing it round. By the time we set off we had quite a crowd who were astounded to see it snake around the factory with relative ease.
Next stage was to build 2 full working prototypes for final testing. The trolleys would also require testing while they are loaded with products. When we were doing this test, we noticed that the system handled much better due to the increased weight. The wheels were able to grip the floor better which meant it took corners tighter than expected which meant we did hit some of the walls during testing. We realised that in a couple of places things would have to be moved which with a full framework on, it would be an issue.
Once approved we made an initial run of 30 units with the anticipation that another 30 would be required once production ramps up to full capacity.
Once they had been in use for 3 months, it was discovered that when making one very tight turn, the trolleys lost stability and one did tip. We assumed from the beginning that a few tweaks would be required once in full usage as this was a very complicated job design and a lot of compromises had to be made to enable a working system. The solution to this though was very straightforward and a limiting bar was fitted to prevent the operator from over rotating when turning a tight corner whilst still being able to make the corner.
Siemens also had to have a company design a bespoke training system for their operators so that they could safely manoeuvre the trolleys around the factory.