You won’t believe what I encountered this week! A well-established home appliance factory asked for my help to reduce energy consumption on their production line because their electricity costs were higher than the raw material costs. Upon inspection, I found that their equipment was running continuously even when not in production, just like someone leaving home with all the lights on. This made me think of many small and medium-sized factories facing similar issues, so today let’s discuss how to optimize energy consumption in intelligent manufacturing using PLC state diagrams.
I remember what an old master in the factory said: “Saving one kilowatt-hour is like saving one yuan, Wen Ge!” This is indeed true. In the current context of rising energy costs, properly controlling equipment operating states has become a key aspect of cost reduction and efficiency improvement in the manufacturing industry. PLC state diagrams are a powerful tool to address this issue.
What is a PLC state diagram? Simply put, it is a flowchart that describes the changes in equipment operating states. Imagine an automatic coffee machine, which has multiple states such as standby, heating, grinding, and brewing, each with different operating modes and energy consumption. A PLC state diagram expresses these state transition relationships in a program, allowing the equipment to intelligently switch based on actual needs.
Last year, when I took over an injection molding production line, I discovered a common problem: the equipment ran at full power as soon as it was turned on, even while waiting for materials. It’s like driving a car and keeping the accelerator pressed even at a red light—what a waste! By introducing state diagram control, we divided the equipment operation into five states: standby, preparation, production, pause, and fault, setting different energy consumption modes for each state.
Let’s look at a specific example. In the state diagram, we can define the state transitions of the injection molding machine as follows:
When the production line receives a "no material signal" for 30 seconds, it automatically switches from "production state" to "standby state"
In standby state, the main motor reduces speed to 30%, and the heating system drops to a maintenance temperature
When the hopper sensor detects "material present", the system automatically switches to "preparation state"
In preparation state, the preheating system starts, but the main motor remains at low speed
Only when the temperature is up to standard and operation is confirmed does it switch to full power "production state"
The core of implementing state diagram energy consumption control lies in precisely defining the transition conditions between states. I recommend using two methods: time-based transitions (e.g., automatically entering low power mode after 5 minutes of equipment idleness) and event-based transitions (e.g., activating a system only upon receiving a specific signal).
On that injection molding production line, we achieved a 23% reduction in energy consumption just through this control method! The boss couldn’t stop smiling.
However, there are some pitfalls to watch out for during implementation. The most common issue is excessive state switching, which leads to increased wear on the equipment. Just like a car that stops and goes uses more fuel than driving at a constant speed, frequent starts and stops of equipment can also create energy consumption peaks. The solution is to set reasonable state transition delay parameters, such as requiring the “no material signal” to be continuously detected for over a minute before entering standby, to avoid unnecessary switching due to temporary situations.
Another common mistake is overlooking system dependencies. For example, when the heating system of the injection molding machine enters low-temperature mode, sufficient preheating time must be reserved to resume production; otherwise, it will affect product quality.The design of the state diagram must balance energy savings with production efficiency, and cannot blindly pursue low energy consumption at the expense of quality and efficiency.
In terms of programming, I recommend using SFC (Sequential Function Chart) to implement the state diagram, as it is more intuitive. Here’s a simplified example code:
STEP STANDBY: // Standby state
SET Main_Motor.Speed = 30%
SET Heating.Mode = "Keep_Warm"
IF Material_Sensor = TRUE AND Material_Delay.Q THEN
GOTO PREP
END_IF
STEP PREP: // Preparation state
SET Heating.Mode = "Pre_Heat"
IF Temperature >= Target_Temp AND Ready_Signal THEN
GOTO PRODUCTION
END_IF
Safety reminder: When implementing energy consumption optimization, do not arbitrarily modify equipment protection parameters. I have seen people lower the minimum pressure value of the hydraulic system to save electricity, resulting in damage to the sealing rings, with repair costs far exceeding the saved electricity costs.
Finally, I want to say that energy consumption optimization is not a one-time task. It is advisable to incorporate energy consumption data collection functions into the state diagram to monitor energy consumption in real-time under different states, providing a basis for continuous optimization.Data-driven energy management is the direction of development for intelligent manufacturing, and even old equipment can achieve “new vitality” through reasonable state control.
If you are also troubled by energy consumption issues in your factory, why not start with one production line, use state diagrams to sort out equipment operating modes, identify energy waste points, and I believe you will achieve unexpected results!
