01 March 2008
Any world-class manufacturing business is really a single system made up of a number of elements. In the days before computers, manufacturing and executive-level elements were closely interconnected by paper trails. As the different parts of the enterprise have become computerised, however, a disjoint between enterprise and shop floor business elements has arisen. Or, more accurately, as enterprise and shop-floor systems have grown, the connections between them have not kept pace, leaving a chasm to be bridged. According to Satoshi Takeda, manager of the controller marketing section at Mitsubishi Electric’s MELCO Nagoya Works, present networks in manufacturing enterprises exhibit a disjoint between enterprise management systems operated by information technology (IT) departments and production management systems on the shop floor. Historically, integration of business systems has gone forward independently of integration of automated systems. At the enterprise level, networking involves development of a massive intranet made up of personal computers and workstations under the auspices of information technology departments. These intranets link directly to the World Wide Web through carefully constructed and maintained firewalls. At the shop floor level, on the other hand, individual automated machines operate independently, sharing data or control signals over a number of factoryautomation network protocols. The present challenge for factory automation engineers is integrating shop-floor islands of automation together and into the enterprise-level.Asahi beerThe present state of automation at theshop floor level is fairly complete in world-class operations. A case in point is Asahi Breweries Suita Brewery in Osaka. Like most production facilities, this brewery’s factory automation network is organised in layers. At the lowest level, individual machines act as complete work cells. Each machine has its own analogue and digital sensors to monitor process variables, such as temperature. Values from these sensors are the starting points for control loops orchestrated by programmable logic controllers (PLCs). The PLCs provide actuator control signals, such as to turn heaters on or off. This is the fieldbus level, which at the Asahi Brewery runs over the CC-Link network. At the next level, the brewery uses Ethernet to tie the individual PLCs together with a supervisory control and data acquisition (SCADA) system. The SCADA systems’ primary functions are to gather process and production data for management review and archiving; provide control information to keep all the individual workcells coordinated; and monitor the entire operation for anomalies requiring human intervention. Should human intervention be needed, the SCADA system issues alerts and instructions via wireless communication. ‘We have gone entirely to wireless because we don’t want our technicians tied to land lines,’ says Yutaka Henmi, manager of the engineering section at Suita Brewery.‘Each technician carries a mobile phone that the SCADA system can call. It can also send text messages with detailed information on the problem and instructions on how to fix it.’ In addition, each mobile unit is equipped with global positioning system (GPS) as well. ‘Since we have so few workers covering such a large area, we must be able to track where each worker is and exchange information with them at all times,’ Mr. Henmi says.The next level: eFactoryWhile world-class manufacturing operations have linked earlier islands of automation together through the SCADA level network, communication links with the enterprise level are still problematic. The problem, according to Mitsubishi’s Mr. Takeda, is that existing manufacturing execution systems (MES) use a classic ‘gateway’ architecture. To gain access to this vital data, management must manually create queries to SQL databases that concentrate and archive it. Such systems bog down as the manufacturing operation gets bigger and generates more data. Gateway architectures are also very expensive to develop and maintain. There are too many system levels to go through and it becomes hard to integrate raw control data into server-side procedures. The result is factory management that does not operate in real time. Nagoya Works has pioneered an integration approach it calls ‘e-Factory,’ which fills the gap with a ‘MES Interface Module’ (MIM). This module is a software system running on a personal computer that communicates with both the enterprise and shop-floor networks over Ethernet. The MIM software can reside directly on a Mitsubishi Q series PLC backplane, where it has direct access to process data generated in the normal course of operation by PLCs at the fieldbus level. It automatically captures data in real time and uploads it directly to the enterprise level MES database. There it is instantly available to the MES applications that align factory operations with enterprise goals. For example, a SCADA system can coordinate production line speeds for components A and B with the assembly line that combines A and B into assembly C, maximising productivity while minimising work-in-process inventory. What happens, however, when a big order comes in? Management would like to speed up all three lines, but, because of the present lack of real-time visibility into what is going on at the shop-floor level, they don’t really know if they can.The e-Factory system provides the needed real-time visibility, so if management ‘sees’ the plant is operating at 80% capacity, ramping it up to, say, 90% allows them to rapidly fill the order without delaying shipments to other customers. Lacking this visibility, the enterprise cannot react quickly to changes in customer demand without maintaining expensive inventory of finished goods. Inventory represents a dormant capital investment, which increases the base for the return-on-investment (ROI) calculation so near-and-dear to company owners. No wonder management teams in large, world class enterprises like Mitsubishi and Asahi are so keen to extend automation throughout their operations. Linking enterprise resource planning (ERP) and manufacturing execution systems to shop-floor automation in real time has a strong positive effect on the business operational efficiency. More efficient operations make better use of their resources, and react faster to changing business conditions.C.G. Masi, Control Engineering
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