Quality Scan: Standards Provide Hidden Benefits
During my 20 years as a controls engineer, I've had the opportunity to see how standards provide great benefits to users of control products. Standards save time in training, installation, and troubleshooting.
In the world of control systems, there are three main groups of standards:
- Manufacturer-specific standards, characterized by multiple users and no local or international standardization.
- Industrial standards (de facto standards) that are in practical use by many users and different manufacturers, but offer no local or international standardization.
- Open standards, which are independent of one specific manufacturer, and are nonproprietary. Generally known/public interfaces exist, and national or international standardization has been completed and published.
About 40 years ago, the RS274 G-code and M-code standard established a common standard outlining how motion is programmed for CNC controllers. The simple, clear structure made it easy to train people, so it became a heavily used standard in NC programming. The new Step-NC standards were developed because today's CNC has many more functions. However it will take much longer for Step-NC to get the same acceptance as G and M code, because Step-NC deals with more complex rules and syntax definitions made for CAD/CAM software. Today, few customers use these solutions, as a higher training effort and skill set is required—so the industry is still seeking a justification for STEP-NC's broad use.
Another standard was, and is, the ±10 V interface between motion controllers and the electrical/hydraulic drive systems. Early on, it was easy to understand, learn, and troubleshoot. Higher performance required higher resolution A/D and D/A converters, however, resulting in drift, noise, and wiring issues. Consequently, the digital SERCOS interface standard IEC 61491was introduced in the late 1980s, standardizing digital communication hardware and fiber cables, and resulting in direct cost savings. The 32-Bit interface resolution resulted in highest productivity, and is expected today. Common motion-related terminology, engineering units (metric and English), standard parameternaming conventions, common functions, diagnostics, etc. across different vendors reduced training costs overall. Now engineers and electricians learn one standard, and can understand and support the drives (electrical and hydraulic) built back in 1988 and today.
In the area of PLC controllers, the evolution with the IEC 61131-3 standard comes to mind. Until 1990, PLC users knew only vendor-specific PLC programming. But in Europe, many OEM and end users pushed for more standard PLC programming, resulting in the IEC61131-3 standard. The standard defines PLC programming terminology, display of program languages, structures, methods, etc. Again, engineers and electricians learn the standard once and use it with PLC software from various vendors. Consequently, more and more end users demand IEC 61131-3 based PLC programming.
The members of the PLCopen organization have successfully created standard motion programming blocks and programming methods built on the already commonly known languages of IEC 61131-3.These PLCopen solutions define the functioning across industries so vendors, OEMs, and end users can reduce integration, training, and troubleshooting time. These solutions are proven in many applications, and many vendors provide compliant libraries for users.
The wide use of OPC communication is a good example of a de facto standard. In this case, it's a communication method between applications running on PC operating systems. Many users benefit by linking OPC compliant products from different vendors without the need of extensive training efforts.
There is a clear trend to unify I/O, motion, and safety into a single Ethernet bus solution. During the next 6–12 months, about a dozen different Ethernet-based bus solutions are being pushed for IEC standardization. Each claims technical advantages, but not all are backed by a large number of product suppliers, and some use a few Ethernet components combined with proprietary hardware. It's a given that the Ethernet bus must be able to handle the application. But users should also evaluate whether the Ethernet bus they are considering will provide the broader benefits of a truly Open Standard.
Users can evaluate and choose standards based on technical details, but should not lose sight of the bigger picture in cost savings: reduced training; more efficiency with common languages; healthy competition of many vendors; and broad and global acceptance. These savings come mainly from adoption of Open Standards.
This article was first published in the January 2007 edition of Manufacturing Engineering magazine.