Abstract
A new control system architecture and signal processing strategy has been developed for Automatic Gauge Control (AGC) systems and the associated servo control of roll force cylinders (screwdown). The system is intended for a broad spectrum of applications involving vertical stack (2, 4 & 6 - High) and Sendzimir/cluster mill configurations for cold rolled flat/strip products, in both single stand and tandem mill arrangements. The new architecture is based on high-speed, real-time control techniques carefully coordinated with embedded, programmable hardware. This innovative combination provides unsurpassed performance and control flexibility. This capability is only now available due to the recent advancements in multi-core processing and real-time operating systems with the incorporation of Field Programmable Gate Array (FPGA) technologies. Signal processing functions traditionally and formerly reserved for specialized interface electronics and proprietary hardware is now directly implemented via software programming of the generalized FPGA circuitry, making this new architecture flexible, open and applicable to Commercial-Off-The-Shelf (COTS) technologies. A key motivation of this developmental effort was the realization that older/legacy systems are increasingly difficult to merge into modern factory environments. A method was needed to provide new system technologies that seamlessly retrofit older systems into future expansion plans. A final motivation was to not rely on the contemporary, broadly embraced strategy, of combining dissimilar equipment to form a system, but to base this development on a consistent, fully integrated, commercially available platform.

This is an overview of the newly developed system architecture and the partitioning of the real-time control and signal processing responsibilities among the hardware and software components of the chosen commercially available equipment platform. Discussions concerning the developmental motivations and the evolution of the development process are provided.

1 – Introduction and Historic Perspective
In the cold rolling of flat strip products, the fundamental objective of an Automatic Gauge Control (AGC) system is to regulate the rolled material thickness about a referenced set-point. The AGC performs this task by the coordinated actuation of the roll gap, separating force, strip tension and/or mill speed. The theories and practices involved in AGC algorithms and roll force cylinder control methods are well understood, and not the subject of this discussion. In this paper, the primary focus is on newly developed technologies in the underlying hardware equipment and software techniques that allow AGC actions to be implemented and carried out in real-time.

Over the past 25+ years, I2S, LLC, has supplied over 260 AGC systems worldwide, starting with one of the first microprocessor controlled AGC systems in 1980. Over the years, we have seen hardware/software technologies and their availabilities change radically, followed closely by the evolving needs of our customers; tighter tolerances, increased reporting, and expanded interconnections between the mill’s systems, including a wide range of plant-wide customer provided computer systems. Through the years, a great many hardware/software platforms and technologies have been employed to implement AGC systems, ranging from commercially available equipment to highly specialized, custom/proprietary arrangements. Early systems employed various combinations of discrete analog/digital components and early microprocessor/computer control technologies (e.g., Z80, PDP- 8, etc.). In that era, the lack of commercially available, sufficiently capable hardware was a formidable obstacle. This led some to implement their systems using a combination of available commercial equipment, special proprietary fabricated boards and in some cases, custom, hand-made, wire wrapped cards. These measures were a necessary fact-of-life, given that the available general purpose interface boards were not suited for this class of application, with their associated performance requirements and feature set capabilities.

AGC systems evolved with the prevailing technologies and soon embraced the emerging VME, Multi-Bus and IBM-PC compatible computer technologies, advanced multi-tasking operating systems, graphical user interfaces (GUIs) and a variety of more sophisticated general purpose interface and communication hardware offerings. Unfortunately, much of the commercial hardware still did not fully encompass the specific performance and feature requirements of a complete AGC system. Even so, it was very possible to utilizes these commercial building blocks to field AGC systems able to meet the broader tolerances of that era. To achieve higher levels of performance, suppliers of high-end systems had to, yet again, bridge the performance/capabilities gap with custom/proprietary boards, some employing embedded microprocessors to off-load the computer system’s real-time computational overhead.

Although an acceptable choice to performance minded end-users, custom/proprietary hardware required those same end users to invest in and willingly commit to a potentially perilous de facto marriage with the system supplier, who offered an inconvenient, single source pathway to spares and repairs. Yes, the resulting systems were highly optimized for AGC applications and tended to achieve the highest degree of performance. However and unfortunately, fears of the manufacture’s potential business failure loomed large in the end-user’s view of these seemingly precarious relationships. The system’s only spare/repair life-line hung tenuously on the thread of whether the equipment provider would be in existence (into the perceivable future) and would truly be able to support this custom hardware over the system’s lifetime.

General purpose, Commercial-Off-The-Shelf (COTS) technologies soon became a fixture and an ever present mantra in the market place, suggesting that end-users could free themselves from these de facto marriages, and openly purchase spares and repairs from other suppliers and vendors, thereby circumventing the OEM and liberating the end-user from concerns over the long term viability of the AGC system provider. This was an enticing proposition…but one that had to be weighed against the fundamental objective of the high end user (i.e., high performance AGC capabilities).

Early COTS equipment was developed for, and directed towards, a broad spectrum, high volume market, whose needs and capabilities may or may not have been suitably aligned with the requirements of high performance AGC applications. An AGC system’s requirement for specialized interfacing and signal handling capabilities were still not common among the needs of the general purpose market place. This led COTS manufactures to bypass these niche AGC requirements. AGC suppliers were left to decide whether their product lines would be fashioned to address the high performance needs of their narrowly intended application (and thereby consciously continue to employ certain amounts of proprietary equipment) or would consciously accept potential performance degradations to embrace a more “market attractive” COTS based system.

Interestingly enough, the rapid pace of commercial hardware development, and quick product end-of-life obsolescence, became a mainstay in the unstable computer and electronics industries. It was not uncommon for PC and VME interface boards to be obsolete and unsupported within 12-18 months of their initial unveiling. This caused many COTS based AGC system offerings to have the appearance of a patchwork quilt, of ever changing hardware components and supporting software drivers, with every new system incarnation being incompatible with effectively identical systems provided a year or two earlier. In addition, many qualified and seemingly stable hardware/software platforms were abruptly discontinued (e.g., Multi-Bus), leaving those utilizing these platforms in their AGC system with little hope for extended support.

So much for the alluring and enticing “Sirens’ Call” of the COTS philosophy… These computer industry facts-of-life led many equipment providers to still develop and employ dedicated, proprietary hardware in certain specific facets of their systems. We have been among them. This is not always a bad thing, time has shown that many proprietary systems have yielded a longer (and more stable) effective product lifetime and a higher potential to be supported for extended periods of time (i.e., greater than 5-10 years and upwards of 20 years, in some cases). However, the attractive philosophy of COTS based systems is still a mainstay in the marketing ploys of those suppliers choosing to accept and contend with the “ebb and flow” and uncontrolled whims of the commercial hardware manufactures. And, to be sure, COTS is not only a desire by the end user, there are advantages to the AGC supplier as well. COTS can aid in reducing cost and development time by utilizing the component manufactures expertise and capabilities.

Recent advances in COTS based controllers have now reached levels of capability to be suitably employed in high performance AGC systems. This has become a fashionable trend and a seemingly viable marketing strategy. Commercial motion/numerical control modules and high speed counting systems are often combined within commercial, general purpose Programmable Logic Controllers (PLCs). These open architecture systems utilize specialized application programming of the general purpose motion control module hardware to obtain the specialized control structures required in AGC applications. One downside of using PLC based controllers for AGC is that it locks the end user into the specific make/model of PLC (and the contained specialty modules) that the AGC supplier provides irrespective of the customer’s plantwide PLC requirements. Modern COTS based systems are constrained by the underlying hardware and software architectures developed by their commercial manufactures. These systems are focused on a broad, general purpose, application based market. The underlying issue in all current COTS based systems is that their general purpose hardware arrangements must be suitably reorganized, and their general purpose data flow architectures must be selectively programmed, to meet the fundamental requirements of the computational processing involved in AGC activities. This can lead to a “painted-into-a-corner” architecture that does not lead itself to future development and a great dependence on a limit number of components (which the COTS supplier may change or discontinue at any time).

2 – The Future, Here and Now
So, where does this leave us? Customers don’t like custom parts available from only a single source supplier. Suppliers are not fond of inflexible, commercial system architectures that limit adaptability and constrain the design. What other options are there? As noted previously, over the years, I2S has sold/installed/maintained hundreds of AGC systems in both domestic and international settings. We owe it to our customers and ourselves to find and develop systems that are maintainable and can be systematically upgraded to satisfy needs of the metals industry. The bottom line is that the chosen hardware platform must provide the necessary capabilities and performance. The chosen software platform must provide the required real-time responsiveness, while also supporting the chosen Human Machine Interface (HMI) and Internationally Standardized network interfaces. In the past few years, a new COTS based alternative has presented itself. One that does not constrain the resulting system with a given manufacture’s preconceived views of what hardware arrangements and data flow architectures will be provided or not provided. But one that offers a general purpose, programmable hardware environment, through which software based control, signal processing and data flows can be implemented with ease. This same COTS based alternative supports hard, real-time control and operating system software to assure deterministic responses to real world events and conditions. Further, all standardized network interfaces are supported, allowing a broad spectrum of commercial HMI software packages (often selected/directed by the customer) to be employed.

This is very welcome news.

This new programmable hardware technology provides the ability to implement application optimized hardware with the flexibility of programming. This technology is Field Programmable Gate Arrays (FPGA). FPGA’s are programmable hardware. Integrated, single chip circuits containing millions of programmable gates that can be configured and interconnected for any need. When the code is compiled and downloaded to the target FPGA, the result is a true hardware implementation of the software application. The software configured / programmed hardware operates in a truly parallel nature which leads to extremely fast execution rates (parallel execution with 40 MHz clock speeds). Figure 1 provides an illustration of the internal components and architecture of a typical FPGA integrated circuit.

Figure 1 – Illustration of the FPGA internal architecture and component arrangement.
Complex, real-time, closed-loop servo controls can be completely implemented in this software programmed, single chip hardware framework (often with cycle periods of 250 microseconds or faster!). This “hardware-in-the-loop” concept provides exceptional computational performance. The fact that the hardware is field programmable means that flexibility and future expandability is ensured. The program for the FPGA is downloaded to the chip on system power up, so hardware updates are as simple as copying a file. Further, identical commercial boards containing the FPGAs, can be placed within the same computer and independently programmed with completely different hardware applications. This means that only a single, commercial hardware component will support the entire needs of the intended application, requiring only a single spare.

The approach presented here employs commercially available programmable hardware to specifically implement optimized signal processing and control architectures. This allows focus specifically on the issues and requirements inherent to AGC activities. There is no need to distort and contort general purpose commercial hardware (e.g., PLC, motion control equipment, etc.) to provide the required AGC capabilities. Formerly proprietary hardware and software are now replaced with programmed, general purpose commercial hardware, programmed via a commercial, open-architecture development language (i.e., National Instruments LabView). A great advantage to this approach is that the system is not restricted to an unyielding, single hardware system architecture. With very little setup time, this same system can be implemented as a PCI bus based computer solution or as a distributed, modular, selfcontained, compact remote I/O system (as shown in Figure 1).

The chosen programmable hardware platform coexists with a real-time controller, allowing dual/parallel processing activities to be used. Using recently released multi-core CPUs (e.g., Intel® CoreTM2 Duo Processors) system overhead is greatly reduced. This means sophisticated control algorithms can be used without worrying that the system will become overloaded. Key features of the FPGA/Multi-core CPU based AGC are:

• Virtualized hardware provided by FPGA versatility
• FPGA hardware interface to the mill I/O devices allows unprecedented flexibility without any speed limitations
• Multi-core CPU’s allow advanced parallel processing to be used without being penalized for computational overhead
• Gigibit Ethernet interfaces to commercial HMI packages eliminate bottlenecks in operator interfacing
• OPC and TCP/IP interface are fully supported
• COTS hardware with multiple configuration options
• Internationally standardized Hardware Description Languages (HDL) provide complete portability to a variety of manufactured FPGA hardware systems (e.g., National Instruments, Xylinx, Altera, etc.)
• Minimal hardware spare requirements

This architecture is not limited to AGC systems or the rolling mill industry. Technologies involving commercial FPGA hardware coupled with real-time control software are popular in a wide range of industrial settings. These controllers are extremely general purpose and I2S is currently employing this same FPGA and real-time technology in its Isotope/Gamma and X-Ray Gauging Systems. Many manufactures of FPGA based, general purpose equipment are introducing a broad spectrum of compatible hardware. This offers an open market of commercially available boards and systems, all of which can be interchangeably used in these classes of applications. This fact alone should alleviate any fears that this equipment is just made for some niche market and may become obsolete in short order.

3 – System Architecture and Implementation
Figure 2 provides a block diagram illustration of the I2S FPGA AGC architecture. Figure 3 provides a hierarchical view of this same system. The I2S AGC system is composed of two primary components: I2S AGC Controller – This Intel® CoreTM2 Duo Processor based computer provides the real-time AGC functions, roll force cylinder servo controls, and high frequency data acquisition for SPC analysis, reporting, and general data acquisition (often coupled to IBA data logging systems). Real-time activities are performed by the National Instruments Real-Time LabView ETS software system (executing on a PharLap Real-Time Operating System supporting symmetric multiprocessing for the Core 2 Duo processor). This controller interfaces to the other control system computers (PLC, HMI, Drive System) via a Gigabit class Ethernet network interface. Precision digital wrap counting is provided from the counting of the quadrature pulse trains of the winder motors’ pulse tachometers / rotary encoders. The controller is housed in a hardened, industrial, 19 inch rack mounted chassis, incorporating a single board Core 2 Duo computer, passive PCI bus backplane and FPGA boards. I2S AGC Human Machine Interface Computer (HMI) - This Windows-based PC compatible computer provides interactive, graphical user interface screens that support the I2S AGC Controller and the HMI software operations. The user interface typically consists of a high resolution, flat panel video monitor (often mounted on/in the Main Operator Desk), a keyboard and pointing device (i.e., mouse, trackball, etc. – depending on customer preferences). The HMI is programmed with commercially available (off-the-shelf) software packages (e.g., WonderWare, Intellution, Cimplicity, WinCC, RS View, etc.) and is open to customer modification and adjustment. HMI data exchanges with the PLC and other control systems (AGC Controller, Drive System, Gauging System, AFC, etc.) is provided through a networked interface via Internationally Standardized OPC Server executing within the HMI computer. All AGC parameters, set-up, calibration, tuning, monitoring, scheduling and utilities are orchestrated through the screens of this interface. All mill management (pass scheduling, coil set-up, roll cluster/stack utilities, etc.) and quality recording, analysis and reporting (SPC/QC) are performed by this computer and the screens supporting these functions. Fault and permissive annunciation are provided by screens supporting these functions. Report and document printing is provided via the networked color printer. Depending on the customer selected HMI package’s capabilities, multiple language support is typically offered.

Figure 2 – Simplified block diagram illustration of the typical AGC system components and their interconnection for a reversing, vertical stack, 4-high mill arrangement. It is important that this same architecture is applicable to Sendzimir/cluster, 2-high and 6-high mills.
The primary sub-components are as follows:

Servo Controls for Roll Force Cylinders

Real-time, closed-loop servo control of the individual cylinders is provided by PID loops implemented and executed within the FPGA hardware (Hardware-In-The-Loop). These hardware based controllers execute in a parallel fashion every millisecond.

Gauge Interface

Sixteen(16) bit A/D converters accept gauge deviation signals (from the thickness measurement systems) directly into the FPGA where they are signal processed and provided to the AGC algorithms.

Encoder Interface

Quadrature pulse trains generated from entry/exit strip measuring rotary encoders are accepted and signal processed to render precise indications of strip length and speed. Wrap counting and roll bite slip angle measurements are provided by quadrature pulse trains generated by the winder and mill motor shaft mounted rotary encoders. No dedicated counters are needed for the encoder interface. Since the encoder signals are fed directly into the FPGA with a 250 microsecond sample time, quadrature decoding is performed directly within the FPGA. The nature of the FPGA programming means that basically an unlimited number of high precision (native 64 bit) counters are available for use (e.g., wrap counting, roll bite slip angle, etc.). The encoder interface functions as a Hardware-In-The-Loop component, supporting the various closed-loop gauge control and automatic slow-down activities.

Gauge Control Equations

The gauge control equations used to render exit material thickness correcting roll gap adjustments are located in the system according to their need and processing requirements. Some components (e.g., realtime transport lag buffering) reside in the FPGA, while others are performed in the Core 2 Duo processor which is under control of a real time operating system kernel (Phar Lap ETS).

HMI User Interface

The AGC system’s graphical user interface is provided by a general purpose, commercial HMI package executing on a separate Windows-based computer. The connection to the real time system is via a gigabit Ethernet interface. The system is fully OPC compliant (an internationally recognized interface standard), offering the ability to accommodate a broad range of commercial HMI systems (e.g., WonderWare, Intellution, Cimplicity, WinCC, RS View, etc.). Since the HMI package is often customer directed, this is a highly advantageous arrangement.

Interface to the Mill’s Master Controller

The AGC system’s real-time controller and HMI computer interface to the mill’s master controller (PLC) via a high speed, Ethernet based network employing the internationally standardized protocols and transmission mechanisms / servers (e.g., OPC, TCP/IP, Modbus, etc.). The PLC functions as the mill’s provider of logic, permissives, interlocks, sequencing, coordination, mode selections, nominal gauge/tension sets, etc. The PLC serves as a system-wide data hub allowing convenient data exchanges between the mill subsystems. The I2S AGC system can be interfaced to virtually any commercial PLC that supports international standards (e.g., Siemens S7-400/300, GE Rx7i/3i, Allen Bradley Contrologix, etc.).

Figure 3 – Hierarchical block diagram illustration of the typical AGC system components and their interconnection from a network topology perspective.Within the AGC’s real-time controller, the new AGC system architecture employs two identical FPGA hardware systems along with a Core 2 Duo processor running a real time operating system (Phar Lap ETS).

Roll Force Cylinder Servo Control FPGA

This FPGA hardware is programmed to interface with the roll force cylinders, including position encoders, pressure transducers and servo/proportional valves. The closed loop control of the cylinders is performed in the FPGA as a Hardware-In-The-Loop component, communicating with the real-time control components via bidirectional DMA transfers.

Encoder Interface FPGA

This FPGA hardware is programmed to interface with the rotary encoders on the mill. These include encoders for AGC, wrap counters and mill motor. The flexibility of the FPGA allows basic counting as well as ratio and speed calculations. The gauge analog deviations and SPC/QC real-time data acquisition transport buffers are also processed through this board.

5 – Conclusion
The history and prevailing issues associated with the supply and sustainable support of the hardware and software components of high performance control systems have been discussed. Optimized, proprietary hardware may yield the best performance, but these desirable technical advantages must be consciously weighed against the realities of a single source supply. The attraction of COTS based technologies must not be allowed to conceal the very real possibility that these general purpose commercial products may not be truly suited for the application at hand and may become unexpectedly modified or discontinued by manufactures focused on a broader market place.

These issues form a classical paradox. The application required performance characteristics are best accommodated by specially designed, custom hardware and software systems, but their single sources of supply are unattractive. Commercially available equipment provides a desirable pathway of supply, spare and repair, but its general purpose designs do not necessarily align themselves with the application at hand.

End users and suppliers find themselves in an awkward position and must make a difficult decision. The key issue has been the lack of commercially available hardware that is appropriately optimized for high performance AGC applications. That is until now…

A new technology has emerged and offers the ability to implement the desired, optimized attributes of customized, proprietary hardware, in the form of commercial, openly available, programmable hardware. COTS based FPGA hardware systems are now commonplace and these programmable systems provide virtual hardware implementations that solve the issues of optimized hardware and commercial availability.

The new I2S FPGA AGC system, described in this paper, has been conceived and developed with the end user and these difficult issues in mind. The first of these FPGA based AGC systems have been successfully installed and are now fully operational on the following mill configurations:

• ZR22-52 Sendzimir / cluster mill rolling stainless steel
• ZR24-8.5 Sendzimir / cluster mill rolling stainless steel and other specialty metals
• Two 4-high mills rolling copper/brass alloys

These systems have been well received, exceeding the customer specifications. This new architecture has fulfilled our design/developmental goals, along with satisfying the performance and supply concerns of the end users, by providing an optimized, high performance AGC system, using commercial, openly available equipment.