16-05-2013, 03:47 PM
FUZZY CONTROL
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CONVENTIONAL CONTROL
Example: design a cruise control system
After gaining an intuitive understanding of the plant’s
dynamics and establishing the design objectives, the
control engineer typically solves the cruise control
problem by doing the following:
1. Developing a model of the automobile dynamics (which
may model vehicle and power train dynamics, tire and
suspension dynamics, the effect of road grade variations,
etc.).
2. Using the mathematical model, or a simplified version of
it, to design a controller (e.g., via a linear model, develop
a linear controller with techniques from classical control).
Performance Objectives:
1. Disturbance rejection properties (e.g., for the cruise control
problem, that the control system will be able to dampen
out the effects of winds or road grade variations).
2. Insensitivity to plant parameter variations (e.g., for the
cruise control problem, that the control system will be
able to compensate for changes in the total mass of the
vehicle that may result from varying the numbers of
passengers or the amount of cargo).
FUZZY CONTROL
Useful cases:
(1) The control processes are too complex to analyze by
conventional quantitative techniques.
(2) The available sources of information are interpreted
qualitatively, inexactly, or uncertainly.
Advantages of FLC:
(1) Parallel or distributed control multiple fuzzy rules – complex
nonlinear system
(2) Linguistic control. Linguistic terms - human knowledge
(3) Robust control. More than 1 control rules – a error of a rule
is not fatal.
FUZZY CONTROL EXAMPLE SERVOMOTORS
• Servomotors are used in many automatic
system including drivers for printers, floppy
disks, tape recorders, and robot manipulations.
• The servomotor process shows nonlinear
properties
• The goal is to apply the fuzzy logic control to the
motor control.
• The task of the control is to rotate the shaft of
the motor to a set point without overshoot.