Page 674 - Mechanical Engineers' Handbook (Volume 2)

7 Effects of Nonlinearities 665

Figure 39 (Continued)(b) Root loci (K u1 1/ 1 ); (c) closed-loop frequency response.

back loop is used to damp an open-loop resonant mode so that higher gains can be achieved
in the outer feedback loop, hard saturation or deadzone in the inner feedback path can cause
the outer loop to become unstable. Similarly, saturation in a feedforward path or in a lead
network can greatly reduce the stabilizing effects they were designed to provide. Another
type of saturation is acceleration limiting. Even if it does not create any stability problems,
acceleration limiting can cause large overshoots when a position servo decelerates into final
position following a large step command.
The resolution of digital systems and certain transducers creates its own set of problems.
As shown in Fig. 41c, resolution nonlinearities can be described as alternating regions of
zero gain and infinite gain. Therefore, resolution will cause most feedback systems to exhibit