Optimizing Performance Design Patterns for Object-Oriented Programming in PLC Factory Informatization
Yesterday, a new device arrived in the workshop, and Old Zhang complained, “This PLC program is too messy; changing one part affects the whole system!” This is not an isolated case. As the level of automation in factories increases, the traditional PLC ladder diagram programming method is becoming inadequate for complex industrial control requirements. Today, let’s discuss how to apply object-oriented concepts in PLC programming to make your programs easier to write and modify.
I remember when I first started in the industry, PLC programs were basically long ladder diagrams, scattered all over the place, and finding an issue required flipping through many pages. Now it’s different; Object-Oriented Programming (OOP) has become an important method in modern PLC programming, especially on advanced PLC platforms like Siemens S7-1500 and Mitsubishi iQ-R that support structured programming. It allows your code to be as clear and organized as building blocks.
What does object-oriented mean? In simple terms, it treats control objects as individual “entities,” each with its own properties and methods. For example, a motor has properties like speed and direction, and methods like start and stop. We encapsulate related variables and functions together to form a “class,” and when needed, we create an “instance” of that class.
Take conveyor control as an example. In the traditional method, you might write:
IF Start_Button THEN
Conveyor_Motor := TRUE;
END_IF
IF Stop_Button THEN
Conveyor_Motor := FALSE;
END_IF
Whereas using the object-oriented approach, it becomes:
Conveyor.SetParameters(Speed:=1000, Direction:=FORWARD);
Conveyor.Start();
Doesn’t it look much cleaner? Moreover, if there are 10 conveyors in the factory, you don’t need to copy and paste the code 10 times; you just need to create 10 instances of the conveyor object, significantly reducing the amount of code.
Design patterns are best practices for solving specific problems in object-oriented programming. In PLC factory informatization, several design patterns are particularly useful:
Factory Pattern: Used to create different types of device objects. For example, you can design a device factory that automatically generates different device instances based on configuration files, facilitating system expansion.
Observer Pattern: Used for monitoring device status. When the status of a device changes, it automatically notifies all other objects that need to know about this change, making it very suitable for alarm systems and data collection.
State Pattern: Manages different working states of devices. For example, a packaging machine may have multiple states such as “standby,” “running,” and “fault,” with different responses to the same command in each state.
In practical applications, what benefits can object-oriented programming bring? In a beer bottling line project, originally modifying a filling parameter required changes in seven or eight places in the code, which was prone to errors. After switching to the object-oriented approach, I only needed to modify one parameter in the filling machine class, and it took effect globally, reducing debugging time from half a day to just a few minutes.
However, there are some considerations when using object-oriented programming in PLCs. First, not all PLCs support object-oriented programming; lower-end models may only support traditional ladder diagrams. Secondly, object-oriented programming can increase memory usage and execution time, so it should be used cautiously in resource-constrained situations.
Additionally, over-design is also a trap. I’ve seen engineers create seven or eight layers of class inheritance, resulting in confusion. Remember, in industrial control, simplicity and reliability should always come first.
How can you practice object-oriented programming in your projects? You can start with these steps:
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Identify the “objects” in the system, such as motors, valves, sensors, etc.
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Define the properties (states, parameters) and methods (actions) for each object.
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Establish relationships between objects (composition, inheritance, etc.).
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Implement these classes in PLCs that support structured programming.
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Use instantiated objects for control logic programming.
For example, Siemens’ TIA Portal allows you to create function blocks (FB) as “classes,” with each instance having its own data block (DB) to store states. In the FB, you can define inputs, outputs, and static variables as properties, and write functional code as methods.
I remember in a project for a pharmaceutical factory, we designed a production line control system using an object-oriented approach. When the client requested to add a sorting branch, we completed the modification in just half a day, instead of the week required by the traditional method. This is the power of object-oriented programming!
Want to learn more about object-oriented programming in PLCs? I recommend first familiarizing yourself with the structured programming features of your PLC, then try modularizing small functional components, gradually transitioning to a fully object-oriented design. Major PLC manufacturers like Siemens, Rockwell, and Mitsubishi provide relevant programming guides that are worth reading.
Object-oriented programming is not a panacea, but it can indeed make your PLC programs clearer, easier to maintain, and more extensible. Next time you modify a program, you won’t have to scratch your head like Old Zhang!
