Fuzzy Logic What is it?

We have received the following question from 'Bill in Edinburgh' and whilst the definitive answer is outside Controls 4 Steam's comfort zone, Malvern at Coulton Instrumentation was more than pleased to assist.

Bill writes:- 

I've just been browsing your products section and I am intrigued by the feature 'Fuzzy Logic' in the Fuji controllers. Can you explain 'What Fuzzy Logic is' Fuji Controllers are in the product section

Malvern replies...

WHAT IS FUZZY LOGIC?
Fuzzy Logic is a simple way to arrive at a definite conclusion based upon vague, ambiguous, imprecise, noisy, or missing input information. In short 'Fuzzy Logic' attempts to mimic human thought process.

WHERE DID FUZZY LOGIC COME FROM?
Conceived by Professor Lotfi Zadeh, at the University of California at Berkley, as a way of processing data by allowing partial membership of a data state rather than a Go/no go state. This was not applied to control systems until the 70's as Professor Zadeh reasoned that people’s highly adaptive control can be achieved if less precise action is taken for a given measurement

HOW IS FUZZY LOGIC DIFFERENT FROM CONVENTIONAL CONTROL METHODS?
Fuzzy logic uses simple rules to control the process instead of trying to mathematically map it. Fuzzy logic is therefore based on the software developer’s experience of the type of system that is being controlled. On a temperature control application the rules may look like this

"IF (process is too cool) AND (process is getting colder) THEN (add heat to the process)" or "IF (process is too hot) AND (process is heating rapidly) THEN (cool the process quickly)"

Or even

"IF (process is too cool) AND (is close to the setpoint) AND (process is getting hotter) THEN (do nothing)" or "IF (process is too hot) AND (process is heating rapidly) THEN (cool the process quickly)"

These terms are vague, but they can describe exactly what the controller should do

HOW DOES FUZZY LOGIC WORK?
A temperature controller working with Fuzzy Logic would compare the actual temperature with the set point to establish how far from the set point the temperature is. Then using predetermined rules, the controller would add more or less heat. By monitoring how fast the temperature changes for a give output change, the controller can use other rules to modify its response.

It is very robust and forgiving of operator and data input and often works when first implemented with little or no tuning.

WHY USE FUZZY LOGIC?

Control output is smooth, despite a wide range of input variations.

Defined rules means that is specifically designed for the process type, i.e. large system lag of temperature systems.

Fuzzy Logic can control nonlinear systems that would be difficult or impossible to model mathematically.

Thanks Bill for your question and Thank You Malvern for your explanation.

Malvern Jones is the MD of Coulton Instrumentation and can be contacted direct at salescoulton.com or visit their web site www.coulton.com for the complete range of instrumentation and control products.