“Difficult tasks in the world must be done while they are easy; great tasks must be done while they are small.”
—— Laozi, Tao Te Ching, Chapter 63
Two thousand years ago, Laozi’s wisdom still shines brightly in today’s wave of industrial automation. When we face production lines stretching hundreds of meters, composed of hundreds of devices, and when program logic is as complex as a spider’s web with rapidly changing signal interactions, this saying seems to be written specifically for PLC programmers. True programming experts are those who understand how to decompose complex systems into simple units and translate grand goals into precise instructions.
1. Simplifying Complexity: The Wisdom of System Decomposition
In modern industrial sites, PLCs are no longer simple logic controllers but the “nerve center” of the entire automation system. I once led a project to upgrade an automotive welding production line: an 80-meter long line integrating 12 robots, 28 sets of pneumatic fixtures, and 5 visual inspection systems, requiring the completion of one white body welding per minute with a failure rate of less than 0.1%.
Faced with such a complex system, using traditional holistic programming approaches would lead to debugging difficulties. Our solution profoundly embodies the wisdom of “doing while it is easy, doing while it is detailed”:
Modular Architecture Design
The entire system is divided into functional domains:
Logistics Transmission Module: Responsible for the precise transport and positioning of the white body between workstations.
Welding Execution Module: Coordinates the robot welding trajectories and process parameters.
Quality Inspection Module: Monitors welding point quality in real-time and establishes traceability data.
Safety Protection Module: Ensures the safety of equipment and personnel in a human-machine collaborative environment.
Each module is further refined into standardized functional blocks. For example, in the transmission module, we adopted a “finite state machine” model to decompose the continuous motion process into 6 clear states: Waiting → Start → Constant Speed Operation → Deceleration → Precision Positioning → Lock Confirmation. Each state corresponds to clear Boolean logic and timer control.
Technical Depth in Details
In the precision positioning phase, we achieved a repeat positioning accuracy of ±0.3mm by using the PID control function of the PLC in conjunction with the absolute encoder feedback from the servo motor. This core algorithm is implemented in just 15 lines of SCL language, yet it encapsulates knowledge from multiple fields: mechanical transmission, electrical control, and software programming:
IF #PrecisionPositioningEnabled THEN
#ActualPosition := #ServoDriver.ActualPositionFeedback;
#PositionError := #TargetPosition – #ActualPosition;
#SpeedSetting := #PositionError * #ProportionalGain + #IntegralCompensation;
#ServoControlWord := LIMIT(MAX:=100.0, MIN:=-100.0, IN:=#SpeedSetting);
END_IF;
This case reveals a core insight: the core competence of PLC programming lies not in mastering complex instructions, but in the ability to decompose complex systems layer by layer, ultimately using simple, reliable code to implement each detailed function.
2. The Philosophy Behind the Technology
When the project was successfully delivered and I witnessed the production line running smoothly like a symphony, I deeply understood Laozi’s saying, “The great way is extremely simple.” The reason why excellent PLC programs can run stably for years is that they adhere to the “way” of industrial automation—respect for physical laws and grasping the essence of engineering.
Law One: Determinism Over Complexity
In safety control loops, we always insist on using verified basic logic rather than complex algorithms. Because when an emergency stop is triggered, the system requires a millisecond-level, 100% reliable hardware-level response. This is akin to “following the natural way”—adhering to the most basic cause-and-effect laws.
Law Two: Fault-Tolerant Design Ensures Reliable Operation
Each functional block is equipped with a complete fault diagnosis and recovery mechanism. For example, when sensor signals are abnormal, the program intelligently decides whether to allow “degraded operation” based on the equipment’s operating status—this context-based state machine fault-tolerant strategy has reduced unplanned downtime by 65%.
Law Three: Continuous Evolution Over Complete Overhaul
An excellent program architecture should possess the ability for continuous evolution. We adopted version management and interface standardization design, allowing subsequent process optimizations to only require adjustments to specific functional blocks without the need to reconstruct the entire system. This “flexibility” embodies the “way”—embracing change within stability and maintaining core principles amidst change.
3. Conclusion: The Cultivation of Technicians
Reflecting on the ancient wisdom at the beginning, “Difficult tasks in the world must be done while they are easy; great tasks must be done while they are small.” The “way” of PLC programming lies in the rigor with which we treat each logical bit, the wisdom of decomposing complex processes into clear state machines, and the ability to maintain a clear architecture even when facing hundreds of control points.
When debugging late at night in the workshop, witnessing the robotic arm moving precisely along the programmed trajectory, at that moment we realize: we are not just writing code and circuits; we are, through technology as a medium, touching that eternal “way”—transforming chaos into order, simplifying complexity, allowing steel equipment to harmoniously operate according to the rhythms of nature.
This, perhaps, is the deepest sense of achievement for PLC programmers and the most captivating aspect of industrial automation.