The automated storage and retrieval system (AS/RS) at IBM's Mechanicsburg, Pa. distribution center is crucial to the computer maker's logistics capabilities. The 21-aisle mini-load system contains 29,400 storage positions that hold bins of computer parts-some of the bins weigh as much as 500 pounds each. The bins are moved in and out of the storage locations by storage/retrieval (S/R) machines.

After nearly twenty years of service, the system was showing its age. It was difficult to maintain the proprietary control systems that operate the machines that gather and deposit the loads. The system was plagued by sloppy horizontal and vertical movement, and the retractors were unreliable.

'Quite simply, the cranes (storage/retrieval machines) were old and starting to fail on a regular basis,' says Frank Ruszkowski, IBM advisory engineer. 'Obsolete components were also making repairs difficult or impossible. As a result of the excessive downtime, we were losing significant productivity.'

IBM decided to retrofit the system through a combination of logic, positioning and speed controls accompanied by new retractors. Most of the work was completed with off-the-shelf control hardware, including communications devices that allow the end-of-aisle controllers to link to the mini-load storage/retrieval machines. A modular approach to the upgrade also saved many hours of downtime during the transition to the new controls, plus they will be easier to support and troubleshoot. The 21 new retractors are more reliable and have replaced the undependable planetary gear-type transmissions.

'The storage/retrieval machines move much faster now and we are experiencing far less downtime because the system is so dependable,' notes Ruszkowski. 'If repairs are necessary, replacement parts and service are fast and simple.'

The faster moving machines result in improved throughputs beyond the original system's specifications. This increased capability helped to justify the upgrade to upper management.

Before the upgrade, the machines used a system of sensors that would slow the units down to a creep until they reached the final reference position. The aging system required this lowest speed to assure that it would not overshoot the horizontal or vertical positions. An even slower speed was required at the pick up and delivery stations.

Now the new system uses improved controls that have a 'learn' feature that optimizes repeated moves. Final positioning is quick and exact. Move times between the bays were also reduced by 30 to 50% in most cases, resulting in higher throughput performance.

'We are extremely pleased with our new system,' says Ruszkowski. 'It's a major piece of the puzzle in reducing downtime and boosting overall efficiency. And you just can't argue with the results.'