Command Generation for Flexible Systems by Input Shaping and Command Smoothing

DOI: 10.2514/1.50270Aggressive motions are often discouraged when a system has flexible dynamics. Common practice suggests thatsmooth commands, such as S-curves, should be used to drive the system. However, smooth commands cannot beimplementedonsomeactuators,suchastheon/offthrustersusedonspacecraftoron/offvalvesusedwithhydraulicsand pneumatics. Furthermore, smooth commands can lead to sluggish response. A rigorous comparison of smoothand nonsmooth reference commands is presented in this paper. The evaluation is performed by treating smoothcommandprofilesasinput-shapedfunctions.Inputshapingisamethodofreducingresidualvibrationbyconvolvinga sequence of impulses with a baseline reference command. By interpreting smooth commands as input-shapedfunctions, a common criterion for comparing smooth and nonsmooth commands is developed. The results of thiscomprehensive comparison indicate that input-shaped step functions are usually more efficient for reducingvibration than commonly used smooth commands. A portable tower crane is used to experimentally verify thecomparison between input-shaped and smooth commands.