Summary This paper presents a new perspective on the stability problem for uncertain LTI feedback systems with actuator input amplitude saturation. The solution is obtained using the quantitative feedback theory and a 3 DoF non‐interfering control structure. Describing function (DF) analysis is used as a criterion for closed loop stability and limit cycle avoidance, but the circle or Popov criteria could also be employed. The novelty is the combination of a controller parameterization from the literature and describing function‐based limit cycle avoidance with margins for uncertain plants. Two examples are given. The first is a benchmark problem and a comparison is made with other proposed solutions. The second is an example that was implemented and tested on an X‐Y linear stage used for nano‐positioning applications. Design and implementation considerations are given. An example is given on how the method can be extended to amplitude and rate saturation with the help of the generalized describing function, and a novel anti‐windup compensation structure inspired by previous contributions. Copyright © 2015 John Wiley & Sons, Ltd.

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The problem of time-optimal trajectory design for high performance point-to-point positioning system under state and control constraints is considered. The proposed solution takes into account Coulomb and viscous friction. A particular structure for the trajectory is postulated, and conditions for its optimality are proven using the Pontryagin Maximum Principle. The explicit solution for the co-states is found. It is shown that one of the co-states contain jumps, together with two singular arcs. Results for a reallife implementation on a nano-positioning X-Y stage are shown.