Sensors Mag

The Industrial Control System—More Than the Sum of Its Parts

April 22, 2008 By: JJ Thiara

Today's industrial automation market continues to be driven by a complete-solution focus, with emphasis on reduced cost of ownership and increased value for the user. Increasingly, though, users turn to subsystems to save commissioning time and reduce costs.


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Today's industrial automation market continues to be driven by a complete-solution focus, with emphasis on reduced cost of ownership and increased value for the user. Increasingly, though, users turn to subsystems to save commissioning time and reduce costs.

Like the human body, an industrial control system can be broken down into a series of processes, each performed by functionally related components working together to form a complex whole. A layman may walk onto a plant floor and see complete systems at work, but the automation professional takes a step closer to see the individual components that make up the big picture and evaluates how each fits into the process and addresses the unique requirements of the application.

The development of industrial control systems is driven by the needs of large industry segments known as vertical markets (e.g., the automotive, material handling, and food and beverage industries). As you'll see, complete solutions for these markets are essentially a series of specialized components, or subsystems, each geared toward an individual process.

Automotive Welding Applications
When it comes to industrial control in the automotive industry, one of the primary goals is minimization of downtime. A manufacturing line lying idle for just a few minutes can cost thousands of dollars. In no area is this truer than in weld cells, which are notoriously tough on the control components within them. The life expectancy of control components is severely shortened in a welding environment due to the presence of strong electromagnetic fields and weld slag.

Sensors, I/O components, and cabling have evolved with new features—physical and electrical—to help them survive longer in weld cells, thereby increasing uptime for the end user. And while weld-field immunity is not new in sensors, it is being combined with other capabilities, such as extended sensing range, to further increase sensor life expectancy. These technologies, coupled with physical enhancements—including protective coatings, alternate housing materials, and specialized accessories/hardware—are allowing users to apply complete weld cell–control solutions that perform better and survive longer than ever.

All these enhancements work together to form a more reliable sensing solution for weld cells, but the automotive industry continues to look for new ways to increase uptime, reduce costs, and streamline maintenance. As a result, there is a growing trend to create subsystems that actually manage the steps within any given process. Currently, the practice for the sensing process in weld cells is to wire all sensors to a central PLC and program the control logic manually. Ideally, future solutions will be pre-programmed systems, where configuration would consist of simply selecting which sensors are active, sequencing the inputs, and enabling user-selectable advanced features, such as sensor diagnostics.

New sensor-mounting configurations and alternate wiring schemes (possibly wireless systems) may further enhance the complete weld cell control system. Sensors would run the gamut from low-priced replacement models to feature-rich versions, with weld-slag resistant construction, self-teach capabilities, diagnostics, and alignment aids. In the end, the complete weld cell control subsystem would be a perfectly scalable and time-saving solution, with a range of products designed to address everything from the low-cost initial installation to the more difficult applications requiring advanced sensors.

The Material Handling Industry
Material handling OEMs strive to provide conveyors that maximize throughput, and they continue to search for control solutions that achieve this goal simply and cost-effectively. Because different conveyors require varying levels of industrial control, a single solution may not include all of the desired functionality for one installation but might be overkill for another—albeit similar—application. As a result, solutions for specific areas have been developed that can be integrated to create an overall warehouse solution—put simply, a full warehouse control solution, comprising a set of complete subsystems. This is most evident in the control systems of accumulation conveyors.

An accumulation conveyor is one that controls the flow of the materials on it to optimize throughput while preventing collisions between the packages being conveyed. The control system achieves this by driving and/or stopping multiple independent sections called zones. Zone control logic dictates how each zone behaves, based on feedback from the other zones.

Traditionally, zone control systems consisted of standard photoelectric sensors hardwired to a PLC, where the necessary logic functions were carried out. But complete solutions have evolved from the traditional approach and now consist of specialized components that allow the zone control logic to be moved out onto the plant floor while allowing for simple plug-and-play installation and interoperability.

Accumulation conveyor zone control solutions can be classified as either basic or complex. Basic zone control manages only accumulation lanes, have no merge or divert sections, and do not perform information gathering. Complex zone control solutions include merge and divert conveyor sections and gather information. Basic and complex zone solutions can be applied as needed for each conveyor section, working together to form a complete control system for the entire conveyor.

In the grand scheme, interacting conveyor control subsystems form the foundation of a material-handling control system that runs the plant floor. This complete plant floor architecture is a combination of conveyor zone control, centralized controllers (e.g., PLCs, PCs), and networks (device- and control-level), all of which governs and optimizes operations. The modular nature of the subsystem approach speeds the development cycle for OEMs and allows plants to get their conveyor systems up and running faster, saving valuable commissioning time.

Exercising Complete Control
Complete solutions, optimized with well-chosen subsystems, not only address the challenges associated with a specific application or industry but also make it easier and less expensive for the user to deploy the solutions. Driven by the needs of larger markets, the solutions ultimately benefit every market to which the technologies are applied by setting the benchmark for improving industry processes while reducing total cost of ownership.


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