What are the differences between fuzzy logic control and PID control?

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Discussion Overview

The discussion centers on the differences between fuzzy logic control and PID control, exploring their applications, theoretical foundations, and practical implications in control systems. Participants express confusion about the necessity of fuzzy logic in comparison to traditional control methods.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that fuzzy logic control seems like an improvement over bang-bang control, questioning its necessity compared to PID control.
  • Another participant emphasizes that the choice between control methods depends on the specific needs of the process, noting that some processes require tighter control than others.
  • A participant points out that traditional control theory, such as PID, assumes linear behavior and known transfer functions, while fuzzy logic does not require these assumptions.
  • One participant describes fuzzy logic control in terms of degrees of control (e.g., "temp is .83cold"), arguing that it appears fundamentally similar to proportional control.
  • A participant references an external article that compares the two control methods, mentioning that both can be applicable in various situations.
  • Another participant notes that the Kreiger Nickoles math associated with PID control can lead to a quarterly amplitude decay, resulting in overshoots before stabilizing at a setpoint.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and effectiveness of fuzzy logic control compared to PID control. No consensus is reached regarding the fundamental differences or advantages of either method.

Contextual Notes

Participants highlight the limitations of traditional control theories, such as the assumptions of linearity and known system behavior, which may not apply in all scenarios. The discussion also reflects varying interpretations of control effectiveness and the implications of overshoot in PID control.

I_am_learning
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I am trying to begin with fuzzy logic, but this initial question is preventing me from moving any forward.
It appears that fuzzy logic control is just an improvement over bang-bang control system. Like instead of doing bang-up , bang-down it does bang-up-hard, bang-up-small bang-down-small etc. It just appears to be discretized proportional control. If it is all about it, we have even better PID control, so why use fuzzy? Obviously I am missing something. Please help.
 
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What your missing is the needed process model. In siuations where close is good enough the bang up bang down method is fine. One example is tank filling.

However there are numerous situations that require tighter control. Some will accept a quartlery amplitude decay. Some need even further dampening to being critically dampened.

The key is the needs of the process.
 
Most "simple" control theory (e.g. PID system design) assumes the behaviour of the system is lnear and its transfer functions are known.

Fuzzy logic system design doesn't require either of those two assumptions.
 
In fuzzy logic control of temperature, you don't say temp is cold, instead you say temp is .83cold, so instead of doing heater on you do heater .83on.
I still find it fundamentally very similar to proportional control.
Can someone show me fundamental difference?
 
Rather than go into th extensive pros and cons of each this article has a well described comparison between the two. In many ways either can be used.

http://www.ece.uidaho.edu/ee/classes/ECE573F05/PID vs Fuzzy Control.pdf

one thing to note that this article does not discuss ifs the Kreiger Nickoles math usually give a quarterly amplitude decay.

thats 4 overshoots each overshoot less each time before it stabilizes on a setpoint. The math gets you close but not critically dampened. critically dampened is no overshoot a smooth transition to set point.
 
Last edited:
Mordred said:
Rather than go into th extensive pros and cons of each this article has a well described comparison between the two. In many ways either can be used.

http://www.ece.uidaho.edu/ee/classes/ECE573F05/PID vs Fuzzy Control.pdf

one thing to note that this article does not discuss ifs the Kreiger Nickoles math usually give a quarterly amplitude decay.

thats 4 overshoots each overshoot less each time before it stabilizes on a setpoint. The math gets you close but not critically dampened. critically dampened is no overshoot a smooth transition to set point.
Thanks.
The article looks just like what I was looking for.
I will read it thoroughly and come with more questions if required.
 

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