Automated Lumber Storage Retrieval System

Background

A major retailer in manufactured lumber required a more efficient means of storing bundles of lumber of various widths and lengths in their warehouse.

The old method relied on a fork truck to place and remove bundles from predetermined piles. The piles had to be spaced far enough apart to allow the trucks to maneuver between them. Wide aisles required for fork truck travel resulted in wasted floor space. A new method was derived using an overhead bridge crane to move the bundles of lumber. By eliminating the need for fork trucks to pass through the aisles, the bundles could be placed closer together, thus reducing the necessary floor space.

System Description
The crane consists of dual trolleys, each with a single hoist. Each hoist contains two forks, which are designed to move underneath the load to lift it. The hoists are controlled by Electromotive IMPULSE^®•VG+ Series 2 drives, which are running synchronization software. The trolleys are controlled by Electromotive IMPULSE^®•G+ Series 2 drives. The trolleys are synchronized by using lasers fed to an Allen-Bradley SLC 5/04 PLC.

The bridge is controlled by two Electromotive IMPULSE^®•G+ Series 2 drives running two bridge motors. The two bridge motors act independently and are controlled to compensate for any skew in the system. Laser feedback to the PLC enables the system to compensate for bridge skew. An Electromotive Anti-Sway unit has also been provided to limit the amount of swing when the bridge and trolleys move the load.

System Operation
Main control of the crane is through an Electromotive radio remote controller with a pendant for manual back-up. The crane works in both manual and in auto-dispatch modes. In manual mode, the hoists, trolleys, and forks have the ability to act individually or synchronized with each other. In auto-dispatch mode, the operator moves the forks under the load and lifts it off the pile. The dispatch location is then selected via the radio transmitter and the dispatch button is pushed. After pressing the button, the synchronized hoists raise, the bridge moves with both anti-sway and anti-skew enabled, the synchronized trolleys position over the pile, and the hoists lower to a predetermined position. After the crane is positioned over its requested location, the operator takes manual control using the radio transmitter and lowers the remaining distance. The operator has the ability to dispatch between the train unload area, the storage piles, the loading area and a saw used to cut the lumber to various lengths.