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Controlling an automated material handling system requires an extensive amount of Programmable Logic Controllers (PLC) or industrial Personal Computer (PC) programming, so that material flow in the distribution center is accomplished in an efficient and well thought out manner. Additionally, with the growing emphasis on energy savings and operational cost control, a smart conveyor system can be programmed to run on demand so as to minimize the power consumption and noise levels.
The typical material handling system utilizes conveyors to transport cartons, totes, boxes or cases through a variety of order fulfillment operations prior to reaching the final destination in the distribution center, the shipping doors. In doing so, there can be diverts to various subsections of the operations such as a forward pick area, dunnage and seal area, value added services, checkweigh scales and sortation for pallet building and staging. In order to successfully navigate these areas, scanners and other sensors are commonly used to identify material and quickly decide where it goes.
There are several steps required in order to properly design the controls for a material handling system. The first step is to develop a sequence of operation, which is simply a narrative explanation of all of the options a product could take as it makes its way from one destination in the distribution center to another. This is also done effectively using a process flow diagram. In either case, the next step would be to identify all of the points that need to be controlled in the material handling system. These control points are typically at sorter induction points, merge points, divert locations, full lane locations, etc. Once these first two steps are complete, then the description of operation, process flow diagram and the system layout with all of the control points is translated into control code.
Typically, for large conveyor systems with motors spread out across the entire footprint, PLCs located inside an industrial control cabinet are used as the primary device for operating the material handling system; whereas an industrial PC is most applied for smaller conveyor systems with limited devices to interface. In either case, a complex but well documented program must be developed by experienced electrical controls engineers. The program must be able to take input from a variety of devices such as photo-eyes, proximity switches and pressure sensors and run real-time algorithms that send output signals to motor starters or divert switches. At the same time, the control system program must also take input from the Warehouse Control System (WCS) or other higher level Enterprise Resource Program (ERP) software so that the control instructions can be applied appropriately. Finally, the status of all input and output devices must be reported accurately to visual displays, databases, the WCS, WMS or the ERP system.
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