6. Fuzzy Logic

• Well suited when we can’t get an exact mathematical model (like we did with Laplace transforms)

• Based on a set of rules, and some fuzzy descriptions about the problem.

• We examine each rule, and each set, and then determine how much each rule applies, and then perform an operation as a combination of the rule effects.

• The fuzzy logic controller works like the PID before (except it does more)










• This methods has been applied to control of servo motors [Li and Lau, 1988].

6.1 Commercial Controllers

• Omron Unit (for PLC)

• 8 inputs, 2 outputs

• 128 rules

• user definable memberships (7 points to define a polygon)

6.2 References

6.1 Li, Y.F., and Lau, C.C., “Application of Fuzzy Control for Servo Systems”, IEEE International Conference on Robotics and Automation, Philadelphia, 1988, pp. 1511-1519.

6.3 Problems

Problem 6.1 Two fuzzy rules, and the sets they use are given below. If verror = 30rps, and d/dtverror = 3rps/s, find Vmotor.


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