Challenge: Safely convey a wide range of unit load sizes between departments to improve quality of product while reducing inventory cost and minimizing operator interface.
As one of the leading manufacturers of high quality wood office furniture, Steelcase was determined to meet the highest standards of excellence in their manufacturing processes and effectuate cost savings. To assure their competitive position in the market place, they installed a group of CNC machine centers, each with full machining capability for all size panels of their wide ranging product line.
The challenge was to provide a reliable safe transport system to handle a wide range of unit load sizes between warehousing, machining and sanding departments. Reliable automatic control of the system was essential; operator interface was to be minimized.
Prior to the implementation of this project many sizes of panels had to be machined and stored in inventory ready for assembly. With the new pallet handling system, generic panels are delivered to the system and quickly manufactured to specification by CNC machines.
The pallet conveyor system, under PLC control, is used to transport loads of panels from the storage area to the machining area, located across a major plant aisle. The pallet conveyor system delivers pallet loads to each machine center automatically and returns pallet loads of machined panels back across the aisle to the sanding department.
In the storage area, unit loads are delivered to the system by order picker trucks and placed on pneumatically operated pallet stands for transfer onto one of two HYTROL CRA pallet accumulation conveyors. Pallets move forward on this staging conveyor for transfer to machining or directly to sanding.
All pallet accumulation conveyors in this system are designed to handle loads 44 inches wide up to 120 inches wide. All loads are 42 inches long. Loads vary in weight from 100 pounds to 4,000 pounds. A split roller design conveyor is utilized with two accumulation zones controlled together with common sensors.
From the storage area, conveyor loads can go directly to sanding or via a transfer cart across the aisle to the machining area. This decision is made prior to transferring the load onto the pallet conveyor by placing a cone with reflective tape on loads that are to go directly to sanding and bypass machining. If a load is directed to sanding, it is transferred by means of a special powered horizontal pivoting pallet conveyor. Once transferred, these loads accumulate on a 26 foot long CRA conveyor and await transfer to the sanding department conveyor system.
Most pallets go to machining prior to sanding. They move by powered transfer cart from the storage area pallet conveyor system to the machining area pallet conveyor system. The machine area conveyor accumulates loads on the lower level and delivers loads to one of six machining centers. Each Heian CNC machine is capable of machining any load sent to it.
Once the load is finished, it is transferred back to the pallet conveyor where it is lifted up to a second level conveyor system by means of a power conveyor mounted on a Southworth lift.
The two level system maximizes the use of floor space and minimizes interference between the pallet conveyor system and the manufacturing function. Once on the upper level, system loads are accumulated and directed back to the transfer cart pick up station for transfer to the sanding department.
Many pallet handling systems were custom designed and incorporated into this system. Reliability of their design was crucial to the system. Equally important was the design and implementation of the controls system.
The control sequence was complex and had to monitor and control the movement of many different size unit loads. A PLC monitors and controls all movement on the system and a combination of proximity switches and photo electric controls are utilized as sensors.
Steelcase was very pleased with the productivity increases and ability of the equipment to perform well.