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A
Model for the Communication of the Product Recipe to the Rolling
Mill Control System for the Production of Long Products
Scott
Stebbing, Rolling Mill Supervisor, Nucor Steel, Nebraska
Hooman
Fazlollahi, B.A.Sc. Quad Infotech, Toronto, Ontario
Khalil
Fazlollahi, Ph.D, P.Eng Quad Infotech, Toronto, Ontario
Copyright
© 1999-2003 Quad Infotech Inc.
Introduction
Traditionally, Level 1 systems have been able to record and save
only single instances of the rolling mill recipes for each currently
running product. Despite their advanced database capabilities
and possession of mill recipes, Level 2 systems in the past have
not been able to effectively communicate with level 1 due to the
cost and complexities associated with creating such links. However,
the industry-wide standardization of OPC (Ole for Process Control)
has changed this.
This paper
focuses on a generic interface model that is able to communicate
with different PLCs. This model enables two-way communication
of mill setup and process parameters between level 1 and level
2 systems.
Recipe information
such as Working Diameter, Roll Gap, Looper Height, etc can be
sent to level 1, eliminating the need for the operator to manually
enter the information and the possible human errors associated
with it. This communication link also allows the level 2 system
to retrieve the mill’s current recipe, or any other process
related variables, at any time and record it in its database.
This will allow future analysis of the data for process improvement
and optimization.
What
is OPC?
OLE for Process Control (OPC) is a new technology designed to
bridge Windows based applications and process control hardware.
It is an open standard that permits a consistent method of accessing
field data from plant floor devices. This method remains the same
regardless of the type and source of data. Therefore, end users
are free to choose the software and hardware that meets their
primary production needs, without having to consider the availability
of proprietary drivers.
OPC components
fit into two categories: OPC clients and OPC servers. A client
is typically a data sink -- an application that uses data in some
way, such as an MMI or SCADA package. A server is a data source
-a device specific program that collects data from a field device,
and then makes it available to an OPC client.
A client interacts
with a server using a well defined OPC interface. Therefore, any
OPC client can communicate with any OPC server, regardless of
the type of device the server is designed to collect data from.
OPC is built
using Microsoft's OLE technology, which is a well tested and proven
foundation. Also, the OPC specification was designed by an open
foundation to meet the general needs of industry - not the specific
needs of a few software or hardware manufacturers. The specification
also provides for a robust evolution of functionality over time,
so OPC components can stay on top of the emerging needs of industry.
How
does OPC make life easier?
Traditionally, any time an application required access to a process
control device, a custom interface, or driver, was required and
needed to be custom written. Because OPC defines a common interface,
a server can be written once, then reused by any business, SCADA,
MMI, or custom software package. In addition, OPC servers can
be easily accessed and controlled from Visual Basic applications,
such as Microsoft Excel macros or Microsoft Access applications.
OPC clients can be written in any current windows development
environment - no special software or toolkits are required.
With OPC,
end users are now able to choose from large pool of OPC servers,
such as those in Matrikon's OPC Component family, to communicate
with their specific devices. They then either develop a client
to communicate with the server, or choose a client such as a Matrikon
OPC Client for their specific application.
What
is QMOS?
Quad Mill Operation System [QMOS] is a comprehensive level 2 system
that provides the production schedule and mill set up for the
production of the mill and captures all the production results
and process parameters on the shop floor. [QMOS] provides the
tools to the mill manager and operators to analyze the production
and setup information and improve the mill set up and production
practices. In this concept providing the latest product set up
information to the mill control system in very important to the
correct utilization of [QMOS] Capabilities.
Functionalities
Provided by QMOS For Recipe Handling
- Ability
to keep and maintain a single recipe database.
- Availability
of the recipes in the level2 system allows easier access by
supervisors for analysis and modifications.
- Ability
to take snapshots of the actual parameters of the mill at anytime
(live recipe). This data could be stored and analyzed later.
- Ability
to gather process parameters on a per-billet basis. These parameters
will be attached to a billet in the QMOS database and can be
accessed later for QC reasons.
OPC
Implementation at the NN2 Mill at Nucor Nebraska
In 2001, the NN2 mill was renovated. The intermediate and finishing
stands were built and installed by Danielli. Siemens provided
the Speed control system for the mill.
Previously,
Nucor kept a copy of the mill recipe on the mill speed control’
repository. At the same time, all the recipe data also existed
in QMOS. The “setup sheets” generated by QMOS were
used by the mill crew to set up the mill at the time of product
change. Meanwhile a different recipe residing on the speed control
system was used for the PLC setup. All missing information such
as roll diameters and grove factors had to be entered manually
from QMOS’ setup sheets. This meant that for each product,
two sets of recipes had to be maintained.
Also, by manually
entering information, there is a greater risk of mistakes being
made in the data entry process, which in turn can cause problems
during the rolling process that may not necessarily be easy to
pin point.
Nucor was
seeking a method to eliminate the redundancy of maintaining two
sets of recipes. As a result, it was decided that a full recipe
for a product and speed calculations for each stand would be transferred
directly from QMOS to Siemens on operator’s command. The
sent information would initially reside on an intermediate location
on the PLC. This data would be cross checked and verified once
more by the operator and the speed control system after the transfer
before it was allowed to be downloaded into the live PLC.
This meant
that QMOS would do the initial speed calculation. With all the
necessary information already available, the speeds and RPMs at
each stand could be calculated and transmitted to the mill control
system.
At the same
time, the sent recipes could be saved in the repository of Siemens
in case QMOS would be unavailable due to any technical difficulties.
However, the primary data repository would always be QMOS.
In addition
to sending recipes from QMOS to Siemens, Nucor also gained to
following functionalities:
- Eliminating
the need for the operator to make any manual modifications to
stand recipes during mill setup. The only modification done
to the recipe involves equipments such as shears since certain
information such as cut lengths normally change constantly.
- Saving
the current setup (actual values) of the mill in QMOS. At any
time, the operator would be able to send the current snapshot
of the mill to QMOS. This information would be used later for
analysis and optimization of the recipes.
- The process
parameters collected per billet. All the process parameters
such as stand speed (actual), R-factor (actual), temperatures
at varying points, and more would be attached to each billet
and saved in QMOS. This information could be used later for
tracing any QC issues or customer complaints.
Product
Family Tree
Product Family Tree (PFT) is the main recipe repository of QMOS.
The PFT holds all the information necessary for the Roll Shop
to schedule rolls and produce setup sheets. This information is
also used by the speed control system to setup the mill.
Scheduling
of Rolls and Passes in QMOS
In the Roll Shop module of QMOS, the lineup of products to be
rolled is available. This lineup is already generated by the Mill
Scheduler. The roll shop operator can assign roll sets and passes
to each stand for each scheduled product.
At the time
of product change, QMOS will use all this information to do the
speed calculation. Roll sets will provide the Roll diameter information.
The pass ID will provide the Grove Factor. The stand related information
such as Gear Ratio will come from the Product Family Tree.
A Walk through
the Product Change routine in QMOS and Recipe Transfer
When QMOS
detects a product change, the following window will automatically
pop up:
This screen will indicate the next product that the mill will
run.
After clicking
“Continue”, the following screen will appear:
This screen
consists of two sections: “Mill Plan” and “Current”
The data under
the “Mill Plan” column displays all roll sets and
passes that the roll shop has planned for the upcoming product.
The data under
the “Current” column displays all roll sets and passes
that are currently in the mill.
The Operator
will decide whether to proceed with the Mill Plan or Current layout.
Next, Pass
Change window appears:
This
window displays the information about the roll sets per each stand
according to the decision made in the previous screen. Here the
operator can make any necessary changes such as changing the roll
set or pass location.
The subsequent
actions taken after this screen, involve the speed calculations
and recipe transfer to the Siemens PLCs.
Recipe Handling
& Speed Calculation (Stands)
The next screen is the following:
This screen
contains two sections: “Master” and “Current”.
The “Master”
section contains all the roll diameters of the roll sets that
were selected by the operator at the previous steps. The finishing
speed and the r-factors are from QMOS’ master recipe repository
(Product Family Tree). Using the finishing speed, r-factors, work
diameters and gear ratios, the RPM is calculated. Also the speed
at the previous stand is calculated using the r-factor. The same
process is repeated in order to calculate the linear speeds and
RPMs all the way to the first stand. The
“Current” section contains the information from the
last time the operator saved a mill’s snap shot. In this
case, the actual finishing speed and actual r-factor for each
stand are used in the speed and RPM calculation. However, if QMOS
detects that there has been a roll change in any stand, it will
transfer the recipe information for that stand from the Master.
Those stands are indicated in cyan color. In this case the theoretical
r-factor value will be used for the RPM calculation of that stand.
Normally,
at the time of product changes that do not require major mill
configuration, it is more desirable for the operator to stay at
the current settings since the mill has already settled down on
a finish speed and r-factor values. In such cases, the operator
will choose to send the ”Current” settings. However,
if most of the stands have been changed due to a major product
change, then the “Master” setting will be sent.
Recipe
Handling (Equipments)
Anything non-stand is defined as an equipment in QMOS. Shears
and roller tables are such examples. All defined equipment settings
can be transferred back and forth between QMOS and the PLC. Clicking
on the “Equipment” button will bring up the following
screen:
Here,
all the equipments related to each stand are defined. For instance,
Stand 1 has two equipments: A pinch roll and a roller table.
The
attributed related to the pinch roll are:
- Selected:
is the pinch roll turned on for this product?
- Lead Factor
Historical
Recipe Snapshots
Pressing the “Other” button will bring up the following
screen:
This screen
displays the previous mill snap shots for the current product.
The numbers of displayed snap shot are user definable. These snapshots
are used mostly for further analysis and improvement of the recipes.
However, the operator can choose to select any of these snap shots
to load into the PLC.
Closing
Thoughts
Using the QMOS recipe management features Nucor Steel managed
to achieve the following:
Single Recipe
Source since QMOS is the single repository for the mill recipes,
supervisors maintain the recipe more consistently and efficiently.
All crews use the same recipe, which creates more consistency
in production and encourages them to pay more attention to the
quality of the recipe. This allows for better startups, more consistent
rolling, less cobbles and higher quality products.
More Up-to-Date
Recipes since the supervisors have easy access to all recipe information
and can make necessary modifications as needed.
Quicker Startups
since there is less need for the operator to search for information
that needs to be entered into the mill control system.
More
Consistent Startups since the possibility of human error is reduced
due to less necessity for manual data entry.
Quicker Section
Achivement since the recipe is more consistent and refined.
Better Recipe
Analysis Tools since a history of mill snap shots are kept in
QMOS for further analysis and optimization.
References:
1. Matrikon
OPC Documents. (www.matrikon.com)
2. [QMOS] User Manual |