By Ellen Fussell Policastro
"Coming from the discrete machine world of PLCs and machine controllers, we talk primarily of programs and tags. We tend to use terms that are common to IEC61131, where they talk about programs, programming languages, functions, and the like. This is the language of machine controller vendors."
As a technology leader at Procter & Gamble in Westchester, Ohio, Mike Lamping believes when guidelines and standards are in production for discrete machine control vendors, machine builders, and end users, the ISA88 terminology in those standards needs to be clearly defined and related to the terms users are familiar with. "Also there may be terms used in the definition of a batch process that do not have common applicability to those in discrete product packaging, like recipes-hence the troublesome terminology," he said.
Lamping is talking about the changes and updates to an ISA88 technical report, ISA-TR88.02, Machine and Unit States. While the committee is in the midst of several efforts: updating Part 1 (ISA88.01, Models and terminology) and developing Part 5 (ISA88.05 Part 5: Implementation models and terminology for modular equipment control), it is the technical report that is causing spirited discussions among committee members. The TR is the report on the work the Make-to-Pack group (part of OMAC) has developed, and describes how they applied the ISA88 models in the packaging industry for machinery.
The discussions between ISA88 committee members center on adding packaging machinery terms into the mix. And because packaging machinery is "not what many people would consider to be batch, in order to apply ISA88 models in this industry, you have to do a mind shift in what you consider units, and what you consider procedures and operations that unit is performing," said Dennis Brandl, president of BR&L Consulting in Cary, N.C., and chairman of ISA88.
"The typical user of batch has been thinking of a unit as multifunction, whereas in packing, the machines are physically complicated but they perform one task, putting stuff in a bag, making a carton, or filling bottles, Brandl said. "In order to apply the ISA88 model successfully, you have to do a mind shift. Much of the discussion was whether that was worth it."
Packaging machinery does not follow the standard rules the committee initially developed on the ISA88 model-operating on the whole batch. In packaging, the machine is moving on pieces as they move through. "So the machine is always performing one primary function," Brandl said. While all these reports have interfaces that are specialized to the vendor, the TR is defining a standard interface to these machines. They're defining a standard set of OPC tags, such as start, stop, and other operations it should be performing. Operations could include producing or going into maintenance or manual mode. "The goal is to reduce the integration time of putting these machines together-the software integration time-so they become much more plug-and-play devices," Brandl said.
Some committee members are reluctant to accept this as an application of the ISA88 standard. But the packaging industry does not use the batch terms and recipe terms in the same way. "This is a communication between systems and equipment. And people are still thinking in terms of recipes, which is a higher level than what's in the standard," Brandl said. "They think when we apply the batch standard to these kinds of machines, we really have to be a little generous in how we define some of the terms. We have people who follow ISA88 religiously. They will say it can't be because it doesn't do x, and in the machine environments that's not the case."
These machines perform one function, or they operate on only pieces at a time. So when filling 10,000 bottles, they only operate on 10 at a time. A lot of people think the batch standard only applies if you are operating on an entire batch at one time. Also the batch standard talks about a deep structure of recipes made up of phases. "In this equipment, a lot of the structure is in the machine itself," Brandl said. "So you tell the machine, 'I want you to perform your primary function, now go.' And you don't see the deep recipe structure that you would see in the process industry. You would tell it to do one thing, and maybe how fast to do it, instead of telling it to do 10 things. So your recipe is a more top-level coordination and parameter-passing method. It's a way to send parameters, such as machine speed, box size, or the amount of material that goes in a bag, down to the devices."
"Applying ISA88 thinking to discrete machines will add order to the myriad of software systems and approaches to discrete machine operation, as well as potentially begin to bring some consistency in a way of expressing data and providing information to higher level systems," Lamping said. Lamping is also chairman of PackML (OMAC packing work group) and editor of ISA-TR88.05.
By using ISA-TR88.05 to apply ISA88 from the batch process to discrete machines, "everyone using PLCs and their own standards will benefit by being able to move beyond designing and training people on the same basic tools, operations, and techniques over and over again with no change in value," he said. "The value of using consistent methods that express machines and their operation in expected functional terminology and equipment decomposition will break old paradigms, lower total costs, and provide the focus on innovation."
Brandl expects the committee will have comments to tie the TR in closer to some of the batch terminology and show the relationships, why packaging is part of the ISA88 standard. There will also be additional diagrams "because this is a communication standard," he said. The additional protocol diagrams will help explain communications between recipe systems and the equipment that will actually work. "Most of these changes are nontechnical to explain the TR better to those people who were not able to attend the meetings," he said. With the updated version finished at the end of February, expectations are a final voting cycle in March.