Automating Manufacturing Systems - Process Control and ...

plc pid - 25.6
θ neural
desired + θ error τ applied
system and
muscles
-
θ actual
arm structure
and dynamics
real world
arm position
eyes
** This block diagram shows a system that has dynamics, actuators,
feedback sensors, error determination, and objectives
Figure 25.5
A Block Diagram
The blocks in block diagrams represent real systems that have inputs and outputs.
The inputs and outputs can be real quantities, such as fluid flow rates, voltages, or pressures.
The inputs and outputs can also be calculated as values in computer programs. In
continuous systems the blocks can be described using differential equations. Laplace
transforms and transfer functions are often used for linear systems.
25.3.2 Feedback Control Systems
As introduced in the previous section, feedback control systems compare the
desired and actual outputs to find a system error. A controller can use the error to drive an
actuator to minimize the error. When a system uses the output value for control, it is called
a feedback control system. When the feedback is subtracted from the input, the system has
negative feedback. A negative feedback system is desirable because it is generally more
stable, and will reduce system errors. Systems without feedback are less accurate and may
become unstable.
A car is shown in Figure 25.6, without and with a velocity control system. First,
consider the car by itself, the control variable is the gas pedal angle. The output is the
velocity of the car. The negative feedback controller is shown inside the dashed line. Normally
the driver will act as the control system, adjusting the speed to get a desired velocity.
But, most automobile manufacturers offer cruise control systems that will
automatically control the speed of the system. The driver will activate the system and set
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