THE INTERNET is on the plant-floor. Web-based technology is now a common tool in many industries, particularly where centralized machine control or process functionality is important. Embedded web browsers are successful in many distributed processes, communicating with centralized monitoring and data evaluation centers. Data streams coming from multiple web-enabled points simultaneously allow operators, on or off-site maintenance, production supervisors, and other connected individuals to observe whats happening at any time.
Data latency isnt an issue in most processes, so delays in delivering information in real-time usually arent a problem. Trending critical events on a polling basis is adequate for most processes. Keeping processes operating within defined high and low limits allows centralized supervisory control to be more effective than scattered, localized control and monitoring stations.
Where genuine real-time information is needed, software layers have been developed to capture data in a defined determinism to provide faster reactive capability.
For instance, as raw materials are converted to discrete product, the need for more real-time information becomes essential. If production processes are disrupted, the raw material feeding that process might keep coming. In a float glass plant, for example, if any of the cutting, separating, stacking and/or packing equipment breaks down, theres no choice but to break glass. Fortunately, glass can be recycled, but many other raw materials converted to off-spec products cant be recycled effectively.
Many machines still operate as fixed automation devices that produce one part or product continually, and are controlled by PLCs. While they excel at providing mission-critical, real-time control, most PLCs arent configured to deliver mission-critical control data at specific times, that is, without adding costly communication modules and a layer of communications software.
On the other hand, many machine control schemes use PC-based control with a real-time operating system and IEC-compliant soft-PLC technology to deliver data because most communication ports (Ethernet, USB, etc.) are built into the industrial PC platform. Adding an Ethernet port to an industrial PC is trivial compared to the sticker shock of adding an Ethernet module to a proprietary PLC platform.
Openness in most PLCs comes at a high price, says David Cole, president of Cole Controls, Ft. Wayne, Ind., a controls integrator for several different machine builders. Either you spend extra money on a PLC CPU card that has a built-in Ethernet card, or you buy a plug-in Ethernet card suitable for data collection.
In contrast, Nick Siliciano, mechanical engineer for Package Machinery, Co., West Springfield, Mass., reports that regardless of the cost and multiple layers of intelligence in his companys machines, his preferred method is to integrate web-based control. We use a common PLC platform with an Ethernet module, then provide a separate HMI platform that includes software for establishing Internet protocol (IP) addresses for each machine, he states.
Similarly, Syscon International (SI), South Bend, Ind., provides manufacturing execution (MES) and monitoring systems for both retrofit and new machine applications. SIs technology monitors and processes mission-critical operating data from injection molding, blow molding, thermoforming, metal forming and other processing machines. Syscon uses a slightly different and more streamlined approach, explains Rick Goldstein, Syscons corporate VP. Syscons PlantStar is a totally web-based technology, says Goldstein. Our strategy is to embed a browser at each machine, deliver that information to our own Linux-based Apache server, then work through the customers IT system by Virtual Private Network (VPN) to deliver the information in virtual real-time. Each intelligent I/O station has embedded pages that provide Down Reasons, Job History, Reject Reasons and other important information. (See Figure 1 below)
FIGURE 1: PROCESS INFO BROWSABILITY
So Lets Browse
The machine environment (See Figure 2 below) suggests theres relatively easy access to machine data with web-based technology. The client might exist at the MES level or at the enterprise level, often, but not always, in the same plant. In many applications, these clients include pages that are delivered by a server somewhere in the enterprise, either locally or from afar. These pages are delivered and stored on the clients. Often using Java applets, page sophistication is determined by the type and amount of information required and the machines complexity.
|FIGURE 2: UNTANGLED WEB|
There can be relatively easy access to machine data with web-based technology. The client might exist at the MES level or at the enterprise level, often, but not always, within the same plant. In many applications, clients include pages that are delivered by a server somewhere in the enterprise, either within the same plant or afar.