Design News for Mechanical and Design Engineers

LOCATION: Dayton, Ohio

ENGINEERING SERVICES: The Engineering and Construction Division of Trimble is focusing on the development of technology and solutions in the core areas of machine control, surveying, and construction instruments.

PROJECT: A complete overhaul of IBM's Mechanicsburg, PA storage and distribution center's twenty-one aisle Eaton-Kenway mini load storage area. Built in 1981, the parts depot consists of twenty-one aisles of mini-load AS/RS (Automated Storage and Retrieval System) and seven aisles of unit load AS/RS. The mini-load AS/RS has approximately 29,400 storage or bin locations. Bins that weigh up to 500 lbs apiece are used to store the incoming computer parts while mini-load stackers store and retrieve the bins. Two levels of pick-up and deposit (P & D) stations at the end of the aisles serve as the P & D points for the bins. Level one is used for replenishment and level two is used for picking. Operators use PCs, also located at the end of the aisles, to direct stacker operation. The PCs are linked to a host computer for order fulfillment and inventory control.

ENGINEERING CHALLENGE: Improve the machinery's overall performance—while simultaneously updating the technology that drives it. After nearly 20 years of wear and tear, the system's operation had become unreliable with obsolete components, making repairs difficult if not impossible. The majority of the control hardware would have to be replaced, and the interface to the host computer redesigned, all with as little impact on the day-to-day operation of the system as possible.

PROPOSED SOLUTION: Rockwell Automation SLC 5/03's to replace the on-board and off-board controllers, use of Trim-ble ICS 5000's and SEW VF inverter drives for horizontal control and Trimble ICS 5000's and new motor starters for vertical control. Finally, 21 new retractors with motors and drives to control the speed of the pin mechanism would be needed. Trimble's Industrial Control System (ICS) 5000 is an industrial positioning system. Using advanced infrared distance measuring and industrial motion control technologies, the ICS 5000 provides exceptionally fast move times, precise positioning, and quick installation. A rugged design (no mechanical parts, shock and vibration resistant) makes the unit highly suitable for heavy-duty industrial environments. The infrared positioning systems, in conjunction with the SLC 500™ BASIC modules, position the mini-load both horizontally and vertically to within 1 mm accuracy.

ANAYSIS: Integrated between the SLC and the SEW motor drive, the ICS 5000 controlling the horizontal axis provides the motion profile directly to the motor drive via an analog speed reference signal. The program in the SLC is simplified by allowing the ICS 5000 to handle the complicated motion control tasks. As a result, the use of a more complex control approach (self learning, closed loop) is possible, while still reducing overall system complexity.

RESULTS: The move times between the bays are greatly reduced (from 30 to 50% in most cases). With the ICS 5000 using the optimal move profile for the system, the crane ramps down to the exact position at the end of each move. A final creep speed and hunting-for-position, common with the previous Tachometer based system, is eliminated. A less obvious, but significant savings is achieved through the ICS 5000's smooth handling of the cranes. The elimination of the harsh deceleration and hunting-for-position greatly reduces the mechanical wear and tear on the crane extending the operating life. A new retractor design gives the reliability desired by eliminating undependable planetary gear-type transmissions of the original table. Their new positioning and drive systems have also improved performance and reliability.