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Control systems apply artificial means to change the behavior of a system. The type of control problem often determines the type of control system that can be used. Each controller will be designed to meet a specific objective. The major types of control are shown in Figure 1.1.

 

 

 Figure 1.1 Control Dichotomy

 

• Continuous - The values to be controlled change smoothly. e.g. the speed of a car.
• Logical - The value to be controlled are easily described as on-off. e.g. the car motor is on-off.

NOTE: all systems are continuous but they can be treated as logical for simplicity. e.g. “When I do this, that always happens!” For example, when the power is turned on, the press closes!
• Linear - Can be described with a simple differential equation. This is the preferred starting point for simplicity, and a common approximation for real world problems.
e.g. A car can be driving around a track and can pass same the same spot at a constant velocity. But, the longer the car runs, the mass decreases, and
it travels faster, but requires less gas, etc. Basically, the math gets tougher, and the problem becomes non-linear.
e.g. We are driving the perfect car with no friction, with no drag, and can
predict how it will work perfectly.
• Non-Linear - Not Linear. This is how the world works and the mathematics become much more complex.
e.g. As rocket approaches sun, gravity increases, so control must change.
• Sequential - A logical controller that will keep track of time and previous events.