Efficient feedforward sloshing suppression strategy for liquid transport

Abstract

Liquid sloshing is typically undesirable in industrial automation, so efficient methods to help avoid sloshing in fast handling tasks involving liquids are vital. This paper presents an advanced feedforward control approach to suppress sloshing dynamics in liquid container transfer robotic systems with a focus on achieving a high-speed transfer of the container. The method integrates three key concepts: First, a virtual suspended tray is introduced, which is a recently proposed approach, to robustly attenuate the sloshing dynamics of fluid-filled containers placed on it. This is achieved by utilizing the tray pivot motion as control input. Second, employing a dynamic model of the tray, container, and the liquid’s sloshing dynamics, a geometric condition is found for the virtual tray/container assembly to fully suppress one specific sloshing mode. This enables rapid container transfers without exciting undesirable dynamics, such as the usually dominant first sloshing mode. Third, accounting also for higher-order sloshing modes, a differentially flat output is derived for the system with a simple geometric interpretation. Hence, trajectory planning of fast rest-to-rest maneuvers of the container which achieve robust and efficient sloshing suppression is facilitated. The otherwise dominant first sloshing mode is entirely eliminated, and all other modeled sloshing dynamics are stopped after any such maneuver. The resulting control law is simple to compute (no optimization or numeric integration of differential equations needed) and achieves outstanding sloshing-control performance. Validation is performed through simulations, high-fidelity finite-element analyses, and experimental tests on an industrial robot. The method is shown to be highly robust in its sloshing suppression even when the liquid filling level deviates from the design value.