If the machine controls in your shop are not interfaced into a plant network and you are comfortable with that situation, you may not get much out of this article. In fact you may ask what's all the fuss about? But, if your shop enjoys the operating efficiencies of controls connected into a plant wide network, then you are aware of its benefits and are probably interested in trends and improvements. AISO7 as more open architecture CNCs are installed and connected into factory Local Area Networks (LANs), the demand is increased for higher data exchange rates in the shop as well as in the office. This article takes a look at the newest and fastest communications standard, Gigabit Ethernet.
There has been a dramatic change in shopfloor communications in the past 30 years. In the past, most part programs have been delivered from the computer room to the machine by hand using reels of punched tape. Even today it is still common practice to hand carry part programs to the machine on floppy disks. This technology, hand carrying of data, has been humorously referred to as "sneaker net." Although it has only been a few years since all shops used the hand carry method, Ethernet technology makes the past seem like the Dark Ages.
Ethernet comes in three versions: 10 Mbps, 100 Mbps, and 1,000 Mbps (gigabit). The main contributors to the success of Ethernet has been its reliability, abundance of available tools, straightforward management, stability, low cost, openness, and its backward compatibility. Each version supports the same CSMA/CD protocol, frame format, and frame size as the original Ethernet standard. This allows Ethernet to offer an open, cost effective and interoperable upgrade solution for organizations when they place their bets on Ethernet technology.
Gigabit Ethernet is defined by IEEE standard 802.3z which was approved in draft form in July 1997 and scheduled to be completed in March 1998. The Gigabit Ethernet Task Force, formed in July 1996, is the organization responsible for bringing the standard to completion. Their key objectives include:
- Half and full duplex operation at speeds of 1,000 Mbps;
- Use of the 802.3/Ethernet frame format;
- Use of CSMA/CD access method with support for one repeater per collision domain; and
- Backward compatibility with 10 Mbps and 100 Mbps technologies.
Where are gigabit communication speeds needed? Skeptics point out that many shops are still happy with systems communicating at 1200 baud to machine tools. But, there is an interesting thing happening in the CNC industry involving distributed control. For years the technical community has talked and promoted distributed control. This is where the intelligence and the computing power is moved as far down in the manufacturing system as possible. With PC-based open architecture controls now entering the picture, many of the conventional desktop functions are now being moved into the CNC. Namely they are third party software packages designed for manufacturing which are best suited for use where they are needed-in the shop. As the amount of data manipulated in the CNC increases, network traffic is also increased and plant networks will need to be enhanced. Also, with the capability to connect PC-based controls to the internet and to intranets, and with the ability to process video, multimedia and 3D models, plant network traffic is expected to increase even more.
Plant backbone networks in many shops are already facing a traffic congestion problem and will be the first to implement Gigabit Ethernet. Their need is being driven by a geometric traffic growth rate not only the result of increased shop activity but also increased desktop activity. With the rapid expansion of intranet and internet use, a network server is likely to be located where most of the traffic must go over the backbone. This inverts the old 80/20 rule of network traffic where 80 percent of the traffic was local, and 20 percent went over the backbone. As network use grows many backbones are soon expected to absorb 80 percent of the traffic in the near future.
Some PC-based CNCs offer Ethernet interfaces for both 10 Mbps and 100 Mbps today or will in the very near future. When will we see Gigabit Ethernet in CNCs? For the moment, there are a number of factors that will delay Gigabit Ethernet interfaces in CNCs. First, 100 Mbps speeds will be adequate for some time in the CNC and second, the cost is prohibitive. But, the communication area is already talking about the next version of Ethernet which is a 10 gigabit network.