Q. Classify Feedback control systems according to purpose of the system?

• Position control systems. Here the output position, such as the shaft position on a motor, exactly follow the variations of the input position.

• Velocity control systems.

• Regulators. Their function consists in keeping the output or controlled variable constant in spite of load variations and parameter changes. Speed control of a motor forms a good example. Feedback control systems used as regulators are said to be type 0 systems, which have a steady-state position error with a constant position input.

• Servomechanisms. Their inputs are time-varying and their function consists in providing a one-to-one correspondence between input and output. Position-control systems, including automobile power steering, form good examples. Servomechanisms are usually type 1 or higher order systems. A type 1 system has no steady-state error with a constant position input, but has a position error with a constant velocity input (the two shafts running at the same velocity, but with an angular displacement between them).