Performance comparison of robust negative input shapers

Input shaping is a control method that limits motion-induced oscillation in vibratory systems by intelligently shaping the reference command. As with any control method, the robustness of input shaping to parameter variations and modeling errors is important. Input shaping has fundamental compromise between robustness and shaper duration, which is closely related to system rise time. For all shapers, greater robustness requires a longer duration shaper. However, if the shaper is allowed to have negative impulses, then the shaper duration may be shortened, at the expense of possible high mode excitation and a small decrease in robustness. This paper analyzes the compromise between shaper duration and robustness for several robust, negative input shapers. In addition, a formulation for specified negative amplitude, specified insensitivity (SNA-SI) shapers is presented. These shapers provide a continuous spectrum of solutions for the duration/robustness trade-off. Experimental results from a portable bridge crane verify the theoretical predictions.