Automating Manufacturing Systems - Process Control and ...

plc pid - 25.7
the desired velocity for the cruise controller with buttons. When running, the cruise control
system will observe the velocity, determine the speed error, and then adjust the gas
pedal angle to increase or decrease the velocity.
Control
INPUT
variable
(e.g. θgas)
SYSTEM
(e.g. a car)
OUTPUT
(e.g. velocity)
v desired
+
_
v error
Driver or
cruise control
θgas
car
v actual
Figure 25.6
Addition of a Control System to a Car
The control system must perform some type of calculation with Verror, to select a
new θgas. This can be implemented with mechanical mechanisms, electronics, or software.
Figure 25.7 lists a number of rules that a person would use when acting as the controller.
The driver will have some target velocity (that will occasionally be based on speed
limits). The driver will then compare the target velocity to the actual velocity, and determine
the difference between the target and actual. This difference is then used to adjust the
gas pedal angle.
1. If v error is a little positive/negative, increase/decrease θ gas a little.
2. If v error is very big/small, increase/decrease θ gas a lot.
3. If v error is near zero, keep θ gas the same.
4. If v error suddenly becomes bigger/smaller, then increase/decrease θ gas quickly.
Figure 25.7
Human Control Rules for Car Speed
Mathematical rules are required when developing an automatic controller. The