Controls/PLC
PLC Controls
In a mechanized distribution center, the PLC (Programmable
Logic Controller) controls all of the I/O (Inputs/Outputs) in
the system. Typical inputs in a system consist of
photoelectric sensors, proximity switches, limit switches and
push buttons. Typical outputs in a system consist of motor
starters, relays, solenoids, horns, beacons and lights. The
PLC reads the status of the inputs, solves an algorithm and
then updates the outputs. The PLC controls all container
flow (flow control, merges, shipping diverts, etc.) from
induction into the system until the container is removed at
its final destination.
PC Controls
In large, high-rate systems, a PC (Personal Computer) communicates with a WMS and receives data from
bar code scanners. The PC then passes container data (container I.D. numbers, size, weight, destination)
to local PLC’s, which in turn handle local controls (diverters, merges, accumulators) used to route the
containers to their final destinations.
Zone Routing
Zone routing conveyor and software provide an efficient means of order selection. Some orders do
not require picks in every zone of a module, so it is important to have a method that will quickly and
accurately determine to which zones a tote should be routed. This is accomplished by use of a
scanner that reads a bar code on each tote as it moves through the conveyor in the pick module.
This information is sent to the host processor, where the optimal path is charted for each tote. The
tote is only routed to the zones containing product needed to fill the order. Other zones are
automatically bypassed.
Merge Control
Material flow must be optimized from the order selection modules to the shipping area in a
mechanized distribution center. In a system where product comes together from accumulation lines,
pick modules and other areas of the system, an intelligent merge controller is needed to maximize
system efficiencies. Each conveyor line that feeds a merge is controlled by a collection of
photo-eyes and package brakes that ensure reliable merging and jam-detection.
Sortation Control
In a mechanized distribution center, sortation control is the nucleus of the system. It processes
shipping, tracking and routing data from bar code scanners and data downloaded
from a WMS, utilizing the data to deliver each package to the appropriate
destination. Once a package arrives at its destination, the sort controller
communicates the package's destination information back to the
WMS so it can be used for bills of lading, invoices and
stock replenishment.
System Monitoring
System monitoring has two basic functions. The first is to
give a graphic overview of the current status of the system,
where individual sections are colored according to their
status. A typical color scheme might be green for running,
yellow for stopped and red for a fault. The second system
monitoring function is to provide the user with a history of
the system through log files if available. Typically, all
communications and changes in faults are time stamped
and placed into this collection of files. These log files are
invaluable in optimizing system performance and
troubleshooting possible errors.
Simulation
Simulation services enable design concepts to be verified and perfected by computer models before
making a large capital investment. It is the representation of a dynamic process in a model that
obtains detailed information about the performance of the proposed system. Computer simulations
utilize the latest technologies that incorporate control algorithms and numerous variables in order
to demonstrate throughput rates and system layout. Data from this analysis is used to develop and
propose a solution that meets the current, as well as future, material handling requirements. The
advantages of simulation are several, including reduction of the investment risk, examination of
critical subsystems, indication of potential bottlenecks, development of emergency strategies, testing
various strategies and definition of performance limits.
WMS Interface
The primary purpose of a Warehouse Management System (WMS) is to control the movement and storage of
materials within an operation and process the associated transactions. Directed picking, directed
replenishment, and directed putaway are the key to WMS. The detailed setup and processing within a
WMS can vary significantly from one software vendor to another, however the basic logic will use a
combination of item, location, quantity, unit of measure, and order information to determine where
to stock, where to pick, and in what sequence to perform these operations. At a bare minimum, a
WMS should have a flexible location system, utilize user-defined parameters to direct warehouse
tasks and use live documents to execute these tasks and have some built-in level of integration with
data collection devices. See DCX Interface below.
ERP Interface
ERP (enterprise resource planning) is an industry term for the broad set of activities supported by
multi-module application software that helps a manufacturer or other business manage the important
parts of its business, including product planning, parts purchasing, maintaining inventories, interacting
with suppliers, providing customer service, and tracking orders. ERP can also include application
modules for the finance and human resources aspects of a business. Typically, an ERP system uses or
is integrated with a relational database system. See DCX Interface below.
DCX Interface
DPI’s Direct ConneX® Order Management and Control Software
(DCX) is a functionally rich suite of software modules designed to bridge
the Enterprise Resources Planner (ERP) and/or Warehouse Management System (WMS) with the machine-level
components and devices in the warehouse. DCX dramatically enhances
the productivity of any system/solution deploying more than one automated technology within a distribution
center/warehouse operation. Direct ConneX® does not replace the ERP or
WMS (such as those written by SAP, Oracle, Manhattan, etc.). Direct ConneX®
augments, improves, and reduces the customization of your ERP and/or WMS systems. What DPI calls
Direct ConneX® (DCX), others in
the industry might call Warehouse Control Software (WCS), Execution Software or middleware.