Robust Feedforward/Feedback Control Logic for a Target-Tracking Mechanical Arm

摘要

An analytic design study is conducted to demonstrate circumstances under which the inclusion of feedforward compensation in a target-tracking control scheme can be expected to offer significant performance gain. In particular, a target-tracking controller design problem for a mechanical arm is developed to assess quantitatively the capacity of feedforward to provide a quicker, more accurate tracking response over wide ranges of uncertainty or variability in the dynamic parameters of both plant and target. The Stanford Aeronautics and Astronautics Department Robotics Lab two-link, two-actuator mechanical arm, inherently a system with variable kinematic and dynamic parameters, provides an appropriate framework for this study. Using recent developments in the theory of quadratic synthesis of robust, low-order optimal controllers, control logic is developed - both with and without feedforward - that enables the arm end point to track a physical target characterized in part by periodic motion of variables or uncertain frequency and phase. It is shown that, using relatively noise-free measurements of target position coordinates only, feedforward compensation can be expected to provide substantial reductions in tracking errors for given constraints on control effort, particularly when the range of variation in target frequency is large.