tags

[peacefighter1996]

Pack-ML state a uniform way of communication making use of tages. However, this is mainly focused on static object structure. This is how most Plc's operate. However Internally we need to look into possible options to communicate properly with an initial data store. with function calling properties.

Thinking what would all be required for the design. I came to the following requirements:

• Must:
  1. Handle Single requests
  2. Handle Batch requests
  3. Provide Internal Structure
  4. Configurable
  5. Communication protocol agnostic (TCP, http, web socket, OPC UA)
  6. Provide methods for retrieving the internal node structures / browsing
• Should:
  1. Bidirectional communication
  2. Cycle based reliable.
  3. Relatively easy to program.
• Could:
  1. Active Intellisense connection.
• Won't:
  1. Deal with access security.
  2. Multi Machine Control

Communication protocol agnostic

Their is one requirement that I highlight Must 5, Communication protocol agnostici. Currently OPC UA is really rising up to be a good way to communicate with machines. And the design of how to implement that framework will probably take quite a few lessons from it. However, It's not the only communication format that is used. And not everyone is using OPC UA. In addition time is quite a big consideration and there is quite some inertia on the way things are implemented within a machine and not every company is trilled to rework their entire codebase or let their machine work in a different way that they are used to. Make the leap to big and people get scared. Secondly, Later we might use a different way of communication between machines then OPC UA. However this portion of the control of the machine should not break if OPC is no longer in use. Based on the lesson of Clean Code.

Security

Maybe this changes in the future. However, there are a multitude of ways dealing with access security and what is more important is that the users of this library can integrate it into their own system. So the expected moment where access security needs to be checked should be before calling any of the functions of this library. A demo might later be developed to demonstrate this concept.

Multi Machine Control

To the same points raised with security. To stay implementation agnostic Its best to not deal with multi machines. With this, I do not meant multi station systems. But sending from one client to multiple different control nodes. This is communication specific thing and deals with the routing of the data. This will not a focus of the library.

Solutions

• Generators
• Data Store Node
• Object Manipulator

Implementation Scenarios:

• Programmer want to provide internal structure.
• Team is in the design phase of the program and want to use Open Pack ML as a basis.
• Need to provide a pack ml interface between the client system and the machine. But the machine is not applicable in a conventional Pack-ML/ISA-88 standard way.