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