Motion technology has been one of the most noteworthy recent improvements in PLC capability, especially in the higher growth nano and micro class of controllers. Many of these low-cost small controllers now include high-speed encoder inputs and pulse train outputs for stepper/servo control at no additional cost. For example, a $199 micro-brick PLC with 36-discrete I/O included (pictured), has built-in capability for two single channel encoders or one quadrature encoder input up to 7Khz, or a single axis pulse and direct output up to 10Khz. This moderate motion performance, at the included cost of the PLC, is a cost-effective solution when compared to a dedicated motion controller paired with a traditional PLC. For the micro modular class of micro PLCs, intelligent I/O modules that leverage the advancements in microprocessors, coupled with the acceptance of Flash ROM, are allowing high-speed motion control modules to be designed as "mini-coprocessors" that use technology developments to provide more cohesiveness between software and hardware. Intuitive graphical configuration software that loads parameters directly to the module''s non-volatile memory can eliminate the need for large amounts of setup logic in the beginning of a user''s program. Implementing these low-cost motion-based PLCs can result in a 2-axis stepper/servo controller application with encoder feedback for under $1200, with input performance of 100KHz and pulse outputs up to 25Khz.
Ideally, open systems can reduce both the initial cost of a control system, as well as the total cost of ownership over its expected lifecycle. Decentralized control, unbundling I/O from controllers, and the use of common networks such as Ethernet can reduce or eliminate the high cost of home-run wiring, multiple junction boxes and terminations between field device and I/O module, and the need for expensive proprietary network cards. Open system controllers, or "WinPLCs," using the Windows CE operating system with an embedded Ethernet interface, give OEMs and system integrators improved software preservation in that their programs can be scaled to target other CE and NT/2000 hardware (operator panels, industrial PCs, etc.), along with a larger variety of networked field devices. This offers tremendous value to customers who are constantly provided the ability to leverage faster processors, to take advantage of price reductions for existing CPUs, and to maintain their application software over time, similar to the consumer PC market trend.
Roadblocks in moving toward open control systems still may be due to interoperability issues between multiple vendor products and the availability of quality technical support for the resulting system. Unfortunately, for the time being, features in one vendor''s product may sometimes be sacrificed when used with a product from another vendor, and neither vendor may have the expertise to provide technical support for this type of integration. This will get better over time, but the difficult balance of single product line and/or vendor source, versus the benefits of multiple product lines and vendors, is still an issue for engineers considering open control systems. It''s worth the effort to seek out vendors that have been offering a wide product breadth of open system products for some time and can qualify the compatibility of their products with others. Additionally, in a day when everyone has a cell phone and a PC with web access, choosing a vendor that can be easily reached by phone and has substantial technical website tools and information (e.g., downloadable manuals, tech notes, customer application forums, etc.) is a consideration when selecting an open control system.
Ethernet as a communication preference across all levels of control and information systems meets the needs of OEMs and integrators who have previously had a tough time satisfying customer demands for connectivity while maintaining a cost structure allowing them to be competitive and profitable. The dramatic decline in the price of Ethernet adapters for PCs has met this challenge, with many PC suppliers including an Ethernet interface on the basic PC motherboard at no additional cost. This means Ethernet controllers and I/O devices can be added to existing Ethernet networks without special hardware. Open control systems with Ethernet now often constitute the ability to instantly connect to other Microsoft-based systems in the enterprise, providing an enabler for any company that desires to implement an "E-manufacturing" structure to eliminate the "automation islands" that often exist between the process portion and material handling and packaging lines.