Also referred to as multi-loop controllers, these are controllers where, in addition to the actual controlled variable such as the position, one or more other variables such as the velocity and/or acceleration are also fed back (Figure K 2). The decisive factor is the type of feedback involved. With the cascaded (multi loop) control system, each controller acts independently and has its own summation point. This means it can be optimised for its own purposes.
A major area of application for cascaded (multi loop) control systems is as electro-mechanical feed drives with servo motors, as used in connection with machine tools. Generally speaking, cascaded (multi loop) control systems have not fared very well compared with state controllers.
Figure K 2: Signal flow diagram for a cascaded (multi loop) control system