Control systems integral to today`s fabs
Open systems, networking and human/machine interfaces blur the lines between traditional control system architectures
By Ralph Rio and Cassius Elston, GE Fanuc Automation
Facilities today must be designed with an eye toward the future. For example, today`s fabs and other types of cleanrooms should be designed to be upgradable for next generation products without disruption to the plant layout and facility systems. This kind of planning requires the implementation of interoperable system technologies and flexible, adaptable control architectures.
Many facilities are turning to automated monitoring and control systems to meet these needs. These flexible systems not only control manufacturing processes, but also ease overall mission-critical cleanroom management — which includes HVAC, power quality, particle contamination monitoring, and more. Typically, each of these areas contains subsystems, each with its own manufacturer-supplied controls. For example, HVAC alone can consist of makeup and recirculation air-handling units, scrubbed exhaust systems, boilers, chillers, and compressors. Equipment and their controls are often by necessity located in different places throughout the facility — which further complicates cleanroom management. By linking equipment into a plant-wide control system and communications framework, the cleanroom facility achieves:
automated and continuous monitoring and response
reduced downtime and increased product quality
high reliability and availability
improved security and plant safety
reduced maintenance costs
integrated, robust computer integration with plant-wide management enterprise systems.
The new demands on fabs require facility systems capable of more than just simple operator responses and button pushing. Considering that the typical estimated durable life span of a fab may be only 20 years, whereas the useful life cycle of the facility control system may reach only 5 to 7 years, it`s easy to see why these systems must be flexible and adaptable. Today`s control solutions must be employed from day one with the anticipation that they will be continuously refined, improved and expanded. New control architectures must meet the demand to be open and flexible. Some of the essential design considerations are:
responsiveness
scalability
openness
ability to migrate
security
reliability
maintainability
configurability.
These systems require detailed analysis and comparison before purchase, or instead of productivity improvements, a cleanroom can face expensive custom software redesigns, communications bottlenecks and hardware obsolescence. By understanding some basic components and trends about control systems — such as network architectures — cleanrooms can leverage the benefits of automation, and design and implement systems that serve well into the future.
Adaptable control systems
Control systems are typically categorized by type of controller. Traditionally, there are three architectures: programmable logic controllers (PLCs), distributed control systems (DCSs), and personal computers (PCs), although as many engineers know, the lines of distinction are not as clear as they were just five years ago.
The PLC can be thought of as a specially designed, industrially hardened computer that gives cleanrooms proven reliability and real-time control in a rugged hardware platform. PLCs have been designed specifically for the challenges of factory control, and the internal architecture is well suited for a wide range of processes and applications. How rugged is a PLC? Many can withstand harsh chemical spills, power surges — even lightning. These controllers are a configurable solution that provides the robustness for reliable automation. Within a typical cleanroom, a PLC could be deployed to monitor clean air, control fans, and supervise energy usage.
The performance of PLCs is determined by a range of criteria including: CPU capacity, scan time, communications capability, I/O capacity and software functions. In most cases, PLCs are modular. To accommodate a new piece of equipment, a cleanroom could simply add blocks or modules of I/O to the existing PLC.
DCSs feature custom control and I/O architectures engineered into pre-designed, self-contained sections and spread throughout a facility. Networks link the various sections together. Because control is spread out and distributed, DCS processing time is typically slower than that of a PLC-based system, and the DCS is less efficient. Furthermore, DCSs require a larger up-front commitment in engineering, resources and money to implement. On the other hand, DCSs have been pre-designed to accommodate specific applications, with much of the point integration, internal logic and operator interface functions already incorporated. In the past, DCS systems comprised the majority of facility automation systems; however, due to their inherent complexity, they also earned a reputation as being less flexible and adaptable. In response to these issues, many of today`s DCS suppliers have turned to more open systems design and standardized I/O.
A relatively new architecture, using common PCs for monitoring and control, allows flexible control systems for even complex applications and advanced computing. Easy-to-use, packaged application software along with the PC`s increased processor speeds, high RAM capacity, and increasing hard disk size position PCs to become a scaleable control system for cleanrooms.
The PC architecture allows engineers to leverage the technology available in the personal computer industry. PCs for industrial control benefit from the continued growth of the multi-billion dollar PC industry and the de facto standards of Microsoft and Intel. Microsoft`s Windows NT operating system is becoming the standard for human/machine interface (HMI) software. Tools such as ActiveX, Open Database Connectivity (ODBC), and Dynamic Data Exchange (DDE) enable the exchange of real-time data across multiple application programs. Data logging, analysis and networking can all be incorporated into a single chassis, reducing the number of system components. Among other potential benefits, there is also the capability to tightly integrate HMI functions and control on a single PC. Additionally, new technologies for communicating to other plant systems are emerging. OPC (OLE for Process Control) is sponsored by Microsoft, and the Semiconductor Equipment Communications Standard (SECS) is sponsored by Semicon. These standards lower the cost and increase the speed of systems integration and application implementation.
When considering applications that require continuous, 24-hour availability, as in most cleanrooms, PC monitoring and control solutions require redundant configurations. Redundancy built into the system reduces risk for mission-critical applications. Fortunately, by introducing distributed, cost-effective PLCs and universal I/O into the PC control architecture, cleanroom facilities can achieve the best of both worlds: the reliability of an industrially hardened PLC and the ease of use and computing power of PCs. This trend toward hybrid systems, and the increasing demands for information, networking and data gathering, demonstrates how improvements in technology are blurring the lines between the three traditional architectures.
One for all, all for one
While monitoring and control systems are still defined as primarily PLC, DCS or PC, there is less rigidity in designs, and facilities are free to combine different types of modules to devise an optimal solution. Several key trends in automation have brought about this change, giving engineers and operators more flexibility with monitoring and control equipment.
Open architecture: For decades, monitoring and control systems were proprietary, meaning that manufacturers produced components that worked only within a single family. DCSs were born out of this philosophy. Today, however, some devices are designed with an open architecture. The controllers, I/O and buses are built to accommodate third-party modules and integrate easily for fast setup. This feature gives facilities the freedom to choose the best and latest technologies from manufacturers without having to stay within product lines or fear product obsolescence. The result is fewer proprietary protocols or systems, improved designs, expanded functionality, and lower cost of ownership.
Networking: High-speed data transfer over networks is critical for the cleanrooms of the future. Advanced communications networks boost productivity and yield. Some companies are now employing advanced computer simulation to optimize the response to changing conditions or manufacturing cycles. Improving response can often translate into fewer defects and ultimately higher margins. Automated material handling systems, which transfer product from one tool to the other, require a much tighter level of integration between tools and processes. Considering that the value of 25 300-mm wafers in just a single front opening unified pod could exceed $1 million, small gains in productivity can be extremely profitable. Additionally, the ability for operators to download recipes and production data reduces set-up time and improves efficiency. With the right networking scheme and control equipment (for example Ethernet), operators can quickly upload and download programs to remote controllers and PLCs, reducing downtime and changeovers. Today, a standard — versus proprietary — network such as Ethernet even allows engineers and operators to access systems over the Internet for remote monitoring and control. This is an ideal way to monitor equipment and access current data, and even involve expert support from a vendor location without the added cost of a service visit.
Human/machine interfaces (HMI) and supervisory control and data acquisition (SCADA): Graphical HMI software provides a Windows-based environment for controlling complex processes. Through an HMI, operators can check the status of equipment and adjust settings from anywhere. The idea of an HMI is that complex systems are easy to use regardless of the control architecture. A Windows-based interface — such as Cimplicity HMI — can be used with a PLC-, DCS-, or PC-based monitoring and control system. Such software provides dynamic, visual display capabilities, including detailed views of any process or operation. Operators monitor and control equipment through the HMI or SCADA — never actually seeing the automation modules at work behind the interface. HMI and SCADA systems also interface with management enterprise systems and management systems for data sharing and reporting.
Cleanroom control considerations
Because cleanrooms require as close to 100-percent uptime as possible, redundancy is a key issue. A facility may choose a DCS or PC-based control system, but PLCs will be the industrially hardened, essential components for mission-critical applications. In many cleanroom systems, hot standby PLCs can protect processes from failure with complete redundancy and permit maintenance without a shutdown.
Additionally, space is always a consideration as cleanroom construction costs rise. Control components, which link into nearly every piece of equipment in a cleanroom, need to have small foot prints. Fortunately, there are compact modules available that also can be mounted on a DIN rail for rackless mounting. Large cabinets are no longer essential for monitoring and control equipment.
Third, because clean rooms include equipment from hundreds of different manufacturers, networking and communications capabilities can be a limiting factor if not considered early in the design stage. Each piece of equipment needs to communicate seamlessly with the control system for effective automation. The development of standard communication protocols, such as SECS, provides a common platform for communications. Developed by the SEMI foundation, SECS is a well-established standard that defines communications between semiconductor manufacturing systems. Adherence to SECS provides a common mechanism for the exchange of data between diverse systems. With a networked system, access over the Internet is possible to simplify and reduce the costs of troubleshooting.
Perhaps most importantly, automated monitoring and control systems provide alarm functions that offer automatic responses ranging from alerting staff with messages on a screen to paging the appropriate engineer or operator. With a log of alarms, cleanrooms personnel can track alarm triggers and identify trends as a means of failure analysis and prevention. Overall, these systems help facilities reduce costs, improve processes, ease maintenance, meet regulations for documentation, and respond to changing conditions.
Lastly, datalogging capabilities in an HMI package permit report generation while networking allows the system to share data, as needed, across operator and management levels. Facilities can record thousands of data points per minute with a full-scale SCADA implementation of software. Data can range from particle levels and temperature, to humidity and vacuum status. With increased information, cleanroom management can analyze trends and implement corrective and preventive measures.
In summary, the capabilities of an HMI that are needed for effective cleanroom control include:
animated color graphics depicting the room and filter system status
alarm management for problem notification
networking for distributed control from many locations
security for restricting an operator`s access to controls and applications (like PC games)
data logging for analysis and process improvement
easy integration with other applications through ActiveX, OPC, SECSII, ODBC, DDE and other standard interfacing technologies.
With an HMI, cleanroom operators can make better decisions in real time when they are most effective — correcting problems before they cause failures. CR
Ralph Rio is manager of Cimplicity at GE Fanuc Automation. He has been involved with solutions for computer integrated manufacturing for 14 years. He has 12 years` experience in factory automation and manufacturing management roles.
Cassius Elston, semiconductor business leader at GE Fanuc Automation, has over 10 years` experience in automation systems and business development. He is implementing a global penetration strategy for GE Semiconductor, an initiative designed to provide the breadth of GE`s products and expertise to the semiconductor industry.
With the right networking scheme and control equipment, for example Ethernet, operators can quickly upload and download programs to remote controllers and PLCs, reducing downtime and changeovers.
 |
Systems not only control manufacturing processes, but also ease overall mission-critical cleanroom management — which includes HVAC, power quality, particle contamination monitoring, and more. Photo used with permission from Intel.
 |
Each piece of equipment needs to communicate seamlessly with the control system for effective automation. Photo used with permission from Intel.
 |
As a universal I/O, VersaMax I/O gives cleanrooms the freedom to connect to a wide variety of host controllers, including PLCs, DCSs and PC-based control systems.
 |
A Windows-based interface — such as Cimplicity HMI — can be used with a PLC-, DCS-, or PC-based monitoring and control system.
 |
Today, a standard — versus proprietary — network such as Ethernet even allows engineers and operators to access systems over the Internet for remote monitoring and control from any location. This is an ideal way to monitor equipment and access current data, and even involve expert support from a vendor location without the added cost of a service visit.