Slimmed-Down Design Snares Hefty Contract

Inside: Rear enclosure of HK3000 houses the PLC and motor drives. Infrared sensors mounted on the machine shut down the system if they detect an object in its path.

The Milwaukee-based equipment manufacturer recently completed installation of 77 automated storage-and-retrieval machines for the Stop & Shop distribution center in Freetown, MA. The clincher: HK's design of a new rotating fork lift machine that delivers the cost efficiency needed to replace conventional fork lifts.

"Companies that use automated storage-and-retrieval systems typically strive for peak performance-pushing equipment for faster speeds and maximum storage density," explains HK design engineer Paul Gines. "For this application, we were challenged to come up with an automated system that would be about half the cost of conventional unit-loading storage-retrieval machines."

Specifically designed for the Stop & Shop project, the company's new HK3000/RF machines move horizontally in both directions on fixed tracks along the aisles. To minimize rack costs for the customer, the machine's rotating fork spears pallet racks, just as conventional forklifts do. However, the machine's vertical lift capability allows it to access pallets just 8 inches off the floor or as high as 40 ft.

"Over the last 15 years, the rotating fork concept saw minimal use," says Gines, the lead engineer on the project. "But now there is a resurgence of interest because customers want to use low-cost pallet racks."

Where small is beautiful

Because maximum throughput was not the goal, the HK engineers could substantially downsize motors, controllers, and gear boxes to keep costs in check. The HK3000/RF uses four variable-speed induction motors from Nord Gear. A 7.5-hp motor propels the machine up and down the aisles, while a 10-hp motor provides the vertical lift for the carriage. Two fractional horsepower motors power the side-shift and rotating movements of the fork mechanism, which allows the machine to transfer a pallet across the aisle to another rack. Contrast this with typical HK automated retrieval systems that use 40-hp motors for moving horizontal and vertical axes.

Aim High: HK Systems downsized motors and controls on the HK3000/RS automated system to compete directly with manual fork trucks and fork turrets. The machine can access pallets situated as high as 40 ft.

The machine must lift light loads that demand gentle handling, as well as heavy loads up to 3,000 lbs. This required use of Commander SE motor drives from Control Techniques for all four axes. "The storage retrieval machines move very smoothly," notes Jose Alvarez, executive VP of Supply Chain for Stop & Shop. "You could put a glass of wine on top of a pallet, and it wouldn't spill."

Also on board the HK3000RF is an Allen Bradley SLC-505 controller, programmed with simple ladder logic and linked to the facility's warehouse management system for move commands. Stop & Shop has also implemented a voice-activation system that directs the machine to stock an empty slot or make other movements. With the huge number of storage positions in the system—more than 11,500 pick slots—HK engineers developed an automatic rack-mapping program so that the machine can find each location and store the address.

While cost control was a clear focus, the new design does not skimp on control and safety features. Two laser positioning devices on the machine interface with the PLC to ensure precise vertical and horizontal movement. The customer also wanted a full-bin sensor array, installed on a lanyard underneath the forks, to scan rack openings and verify that all boxes are removed prior to load deposits. Other sensors in the system prevent tall loads from being deposited in slots with insufficient height.

For safety, the HK3000 employs infrared sensors, supplied by Sick Optic, that monitor an area 30 ft around the machine. The system automatically shuts down if anything is detected in the machine's path.

Gines notes that HK has been "overwhelmed with interest" since the Stop & Shop installation. With prices that are half the $230,000 to $260,000 charged for conventional storage-retrieval machines, Gines believes the HK3000/RS provides a realistic alternative to manual fork trucks and turret trucks.