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Level
II Automation Systems
Manufacturing Execution
Systems (MES) are usually considered to be
the second level of control above the
programmable controller (PLC) or Distributed
Control System (DCS). A hybrid system may
do direct control as well as a MES system
if direct I/O is connected to the system.
However, general purpose computer systems
typically do not lend themselves to this
architecture. Where guaranteed timely
response to real world signals is essential,
a multi-tier solution is typically required.
MES systems typically
perform the following functions:
- Supervisory control
- Track conformance to
plan
- Oversee the execution
of the plan
- Run complex quality
models
- Provide a common
distribution point for correlation of
events and distribution of
information to multiple
MES systems
- Capture and record
event and batch related information
- Create production and
quality reports
- Run complex setup
models
- Use process data to
tune process models
- Statistical Process
Control
- Audit production
results (such as FDA requirements)
- Provide current
process data to down stream processing
units (batch sizes, chemical
compositions, batch completion times,
finish batch temperatures)
- Provide analysis
platform for the practice engineer to
analyze process data
- Execute a production
plan developed by an ERP (Enterprise
Resource Planning) system
- Process Scheduling
- Laboratory
Information Management Systems (LIMS)
MES Environment Support Knowledge
The MES functionality can
be present with computers serving as Human
Machine Interfaces (HMI) that are connected
to PLC and DCS control systems. With the
advent of lower cost relational databases
and more compute capabilities, many MES
systems make use of relational database such
as Oracle and SQLServer. Virtually all MES
systems are networked to other areas and
levels of automation. IPACT therefore has
staff people who are trained DBAs for Oracle
and SQLServer.
Typically the MES systems
are implemented using Microsoft Windows NT,
UNIX, or OpenVMS operating systems. These
MES systems may be implemented as
heterogeneous networks and platforms. IPACT
has knowledge on all of the major operating
systems. This knowledge goes to the level
of programming the system service calls and
even writing kernel device drivers for all
of these operating systems. Typically, this
level of knowledge is not needed when
developing in some platforms such as
Microsoft NT and Windows 2000 (due to their
object architectures). However, IPACT
engineers that are trained to this level of
expertise can diagnose obscure and difficult
problems.
IPACT has staff that
configures and designs networks for the
heterogeneous environment used by many MES
systems. This includes proprietary control
networks such as Modbus Plus and
general-purpose networks such as TCP/IP and
DECNET. This includes the technologies of
Microsoft COM/DCOM, ODBC, sockets, Message
Queues, and RPC (Remote Procedure Calls).
MES Products
There are some off the
shelf packages that allow for tracking,
sequencing, and executing of a plan. IPACT
has used WonderWare’s InTrack and InBatch
products. We have developed front ends and
extensions for the InTrack product.
Additionally, products are available that
display and aid in analysis of data from an
MES system. In particular, IPACT is
familiar with the following products and has
implemented systems using these or
cultivated experience with the following:
Process Analysis Support
IPACT has designed MES
systems that acquire data from the
process. This data is correlated with the
product being produced or simply temporarily
archived. IPACT has provided custom tools
for supporting the storage, display, and
analysis of large volumes of process data.
We are familiar with interfacing with G2 (Gensym),
RS1 (BBN), PI (Oil Systems), and many
personal computer desktop products.
IPACT has written ODBC
drivers that allow PC products to easily
extract historical process data into ODBC
compliant clients. A typical example would
be the import of process data into an Excel
spreadsheet. By using ODBC the practice
engineer can also join data from relational
databases such as Oracle.
Supervisory Control
MES systems are typically
responsible for the set point or recipe set
up for the process based on the product and
current environment parameters. These
supervisory functions might include the
selection of particular lots of raw
materials to be used for making a product,
identifying required quality parameters, and
all process parameters for the control
system. The supervisory control includes
the tracking of product, reporting of
production results to down and up stream
facilities, reporting the consumption of raw
materials, and quality acceptance or
rejection of the product.
Track Conformance and Execution of the Plan
If a schedule is created,
an MES system can track the current
conformance to the plan. This information
can be used to inform down stream systems of
delays in their raw materials. The MES
system can speed up or slow down the process
(within its capabilities) in order to
conform to the plan. The MES system can
forward the production status and results to
ERP systems in the event significant
schedule deviations require additional
schedule revisions.
Run Complex Quality Models
The MES systems typically
have quality specifications available to
them. Additionally, the MES systems also
have the production results, current
operating conditions, and process historical
data. This provides an ideal platform to
develop models that correlate known defects
with operating conditions. In applications
where complete visual or other inspection is
not possible, signature analysis and
deviations of key process variables from
known valid ranges can be used to determine
the expected quality of the produced
product. Additionally some models are able
to correct expected quality problems before
large batches of product are actually
scrapped.
Provide a Common Distribution Point
In a complex facility,
there may be multiple areas of automation.
MES system functions as a focal point
responsible for joining information from
multiple sources such the data can be
correlated to events and the product being
produced. The MES system provides the
tracking information and sequencing for the
different automation centers.
Capture, Record, and Report Production
Events
Most MES systems record
information about the processing being
controlled. This may be quality or
production information. Data must be stored
in an appropriate fashion, for an adequate
time frame, and be available for reporting
and analysis. Some applications such as
pharmaceutical have FDA requirements for
archiving key operating events. Managers
require information about production
results, production capabilities, and job
costing.
Run Complex Setup Models
Recipe creation is on one
method of downloading set points to a
process. However, if the recipe is
dynamically based on the current process
environment, raw materials available, and
desired product characteristic, a set-up
model is typically used. IPACT has worked
with research departments as well as
developed these types of models with their
customers. These set up models may also be
able to predict product completion time
based on practice steps needed to complete
the process. These set up models can also
be adaptive by using their previous
predicted performance and actual performance
to tune model parameters.
Statistical Process Control (SPC)
Both manual and automatic
SPC can be done on the MES systems. Typical
graphical output and alarms can be provided
for the user.
Scheduling
If an ERP system exits, it
typically provides a schedule for the MES system
to execute. There can be an overlap of
functionality between ERP systems and MES
systems. Typically, it is in the granularity
and ability to adapt to process changes where
the functionality of the two systems are
different. Both systems need to understand the
manufacturing model. Once a plan is created,
the MES system needs to track, supervise, and
control the execution of the batches or product
through the production train. IPACT has
assisted in the development of the ERP model.
However, our strength is the design of the
manufacturing model itself and its specification
and execution within an MES system.
An MES system uses current
operating conditions to attempt to execute the
schedule. Machine breakage, cleaning
requirements, resource availability, and raw
material availability affect the ability to
conform to a schedule provided by an ERP system.
Many times multiple process
routes and options are available to create a
particular product. In this type of
environment, the MES system will schedule the
batches that best satisfy the ERP-provided
schedule on the appropriate available machines
or production routes. This is the case where
the granularity of the process is only known to
the MES system. The MES system might choose to:
- Schedule a batch as two
batches in order to meet a production
schedule.
- Delay a batch because
cleaning of a machine would not be required
if compatible batches are run in sequential
order.
- Schedule batches such
that components of a particular batch arrive
at a join in the production route in the
correct order (e.g. work in progress
batches are consumed at an operation where
multiple sub-routes are joined).
IPACT has developed a
scheduling application that is integrated with
Wonderware’s InTrack product. Along with
ActiveX objects, InTouch or Visual Basic
applications can call an object method to
determine what candidate batches queued to a
process operation should be started and on what
machine. The scheduling application runs as a
standalone application which examines current
state of the process, resource availability,
work schedule, manufacturing process model
(e.g. routes, machine capabilities), already
started batches, and all scheduled batches. The
scheduling application can be
reran at any time
to update the currently scheduled batches. The
rules for scheduling are typically custom for
each application. However, cleaning, batch
size, and the number of routes are all taken
into consideration in developing the schedule.
Laboratory Information Management Systems
Many MES systems have a
quality control lab or other system to test
the resultant products for the conformance
to specifications. IPACT has implemented
multiple systems of this type. We have also
interfaced lab instruments and integrated
bar code scanner technology for sample
identification and tracking. Laboratory
results have been fed back into the MES
system to select quality disposition of the
product.
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