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Potentially volatile environment calls for extra features on driverless forklift trucks

Although the factory and warehouse aisles of an un-named UK manufacturer of fast moving consumer goods (FMCG) are not defined as hazardous, some products contain volatile materials that can present an explosion risk. It was therefore necessary to tailor the design and installation of two automated guided vehicle (AGV) systems that have replaced conventional fork lift trucks for transporting palletised loads between two factory areas and a warehouse.

Specialist company E&K Automation won the contract to supply the two AGV systems, each of which uses seven laser-guided vehicles of compact counterbalance design. Both AGV systems are totally independent of each other, although any vehicle can be deployed to work on either system for maximum resilience and flexibility. A further advantage of the twin system approach was that commissioning of phase 2 early in 2011 had no effect on phase 1 AGV operations.

Both systems, which were implemented without unplanned disruption to production, are linked to the customer’s pre-existing warehouse management system (WMS). Two-way communication with the driverless vehicles is via WLAN (wireless local area network).

Safety measures

While the low risk of explosion did not warrant fitting on-board gas detection and shutdown equipment to each of the AGVs, they are all interlocked with factory-wide fire and gas alarm systems and interact with a number of automatic doors.

It was also considered expedient to incorporate features on the vehicles to lessen the chance of product damage that could result in gas being leaked into the warehouse or factory aisles, as well as other measures to guard against ignition of any leaked gas that may be present.

E&K Automation fitted AC motors to power the drive, steer and lift on the battery powered vehicles, avoiding DC motors with their potential risk of sparks from the brushes. To maximise safety during travel, three laser scanners are employed, one at the front, one at the rear and another at high level to detect obstacles on the circuit. Electrically conductive tyres are employed to aid the dissipation of static electricity.

To ensure the AGV knows the precise position of its forks when a pallet is transferred or transported, two rotary encoders are fitted on the lift mast, rather than the normal one. Additionally, each fork tip includes a photoelectric sensor and there’s a further sensor on the forks carriage to detect that the pallet is fully on board the AGV.

Three battery charging bays have been provided in each AGV system to automatically top up vehicle power. In some AGV environments, charging contacts are set into the floor but in this installation, they are mounted on the wall. This approach avoids having the battery contacts close to any leaked gas that might collect at floor level and also removes the need for disruptive building work.

Further safety features

The above measures are in addition to the usual warning and safety features on E&K AGVs for protecting personnel and guarding against damage to the products being handled, all in compliance with European safety standard EN1525 for driverless vehicles operating in a mixed environment.

In addition to the obstacle-detecting laser scanners at front and rear, pressure-sensitive strips stop the vehicle immediately an obstruction in the AGV’s path is touched. Multi-colour status lamps, amber turn-indicator lamps, two types of audible warning device and four emergency stop buttons are standard equipment. About 70 pallets per hour are transported by each system, 24×7, and pallets weigh up to 1.25 tonnes. The AGVs drive at speeds of up to 1.5 m/s, travel up and down ramps and cross a roadway, so safety is paramount.

Choice of AGV system

At the outset, an analysis was carried out by E&K comparing fork lift and conveyor based AGV concepts and mixed fleets. It was concluded that for a robust, reliable, flexible and resilient transportation system that can automatically handle both 1,200 x 1,000 mm Chep pallets and 1,200 x 800 mm Euro pallets at floor level and at various conveyor heights, the use of E&K Compact CBI-800 counterbalance fork lift AGVs throughout both systems was optimal.

This truck format allows pallet transfer positions to be passive, leaving floors clear and free from powered conveyors. It also avoids frames that would otherwise be needed to support a pallet stacker AGV format and wide aisles that would be needed with a straddle stacker AGV. The counterbalance design also means that palletiser conveyor interfaces do not need to be modified to accept the narrow or wide load-wheel-arms that come with pallet stacker or straddle stacker AGVs.

Peter Holdcroft, managing director of E&K in Bramley, Hampshire, commented, "Our COMPACT counterbalance platform has proved especially popular here in the UK.

"It provides a blend of competitive price, small size, high manoeuvrability, reduced weight and lower energy consumption plus stability that complies with the new BS ISO 22915 safety standard for powered industrial trucks.

"In addition to the 1200 mm lift vehicles supplied to this particular customer, we have recently installed similar counterbalance trucks as part of a large system for another customer, in which the AGVs have high lift masts with tilting forks to serve gravity racking. Another customer has the same vehicle, but with a 7.5 metre lift mast.
System operation

In essence, both AGV systems at the FMCG factory are designed to take palletised raw materials and packaging from a conveyor system in front of the warehouse to around 85 passive floor positions in the production areas. Surplus material and finished product from central palletiser conveyors are returned into storage, while waste is taken to a compactor. Positioning accuracy of the vehicles relative to each pick or drop location is ± 10 mm.

There are three levels of control. In normal mode, vehicles operate automatically under central AGV control. In semi-automatic operation, they can be given instructions through on-board or remote terminals. If operated by hand, the AGV is driven and steered manually via its joystick control, with load handling effected by push button.

Vehicle navigation is by E&K’s NAV830 laser triangulation system, which allows even the most complex AGV route including load pick and drop positions to be simply created on a CAD workstation and modified afterwards if necessary. Laser navigation reflectors are fixed to elevated positions on walls, columns or racking. Simulation tools help to optimise the routes, select the optimum number of vehicles and check for conformity with European standards. EK-REPORT provides user-friendly presentations for analysing operating and performance data.

Local, real-time management of each AGV fleet is carried out by an E&K OS830 system, which consists of a system PC (server) at the control level and a number of user PCs or HMIs running Windows at the operator level, with communication via TCP/IP protocol over the customer’s own Ethernet network. Each AGV system has two PC servers with fully transferrable RAID hard drives, so that any of the four PCs can be booted up to run either of the two systems to guarantee system redundancy.

Primary tasks of OS830 include communicating with the WMS, handling transport orders, optimising AGV task allocation, traffic control, communication with the AGVs, and logging and analysis of operating data. Screen graphics show the actual positions on the tracks of all AGVs, which are represented as colour coded icons to reflect their status. A remote access hotline is provided for diagnostics and support.

Conclusion

Summing up the benefits of the installation, Peter Holdcroft pointed to the importance of automation in allowing Western economies to compete with low-wage countries. He said that it was the prime reason for this FMCG customer replacing manually operated lift trucks with AGVs.

He continued, "The flexibility of our latest AGV systems makes them future-proof, enabling extensive modification, upgrading and extension of capacity as circumstances dictate.

"The control system and peripheral equipment are modular and, with laser navigation, changes to the layout are particularly straightforward.

"Moreover, with our CBI-800 counterbalance trucks, the AGV chassis can be fitted with different lift masts as requirements dictate, introducing another layer of system versatility."

E&K Automation is a European market leader in driverless industrial trucks and systems, with over 45 years’ experience in mainland Europe and a 29-year track record in the UK. From group companies in Germany, Italy, the Czech Republic and the UK as well as through partner companies, it has supplied more than 1000 AGV systems employing many thousands of vehicles.

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