Page 651 - Mechanical Engineers' Handbook (Volume 2)

642 Controller Design

Figure 20 Effects of a simple lag compensator on the closed-loop response of a poorly damped system:
(a) root locus; (b) frequency response.

be aware of several potential limitations. These limitations usually involve the higher order,
higher frequency dynamic modes that were unknown or neglected in the early stages of the
design. Examples are structural modes, transducer dynamics, and drive amplifier dynamics.
Higher order modes associated with actuator mounting structure, actuator–load me-
chanical connections, and transducer mounting are usually second order and poorly damped.
Often these modes are characterized as poorly damped pole–zero combinations. In either