Evaluation of a simple anti-sway control without start-up delay and over-travel

This paper evaluates a simple anti-sway control algorithm for fixed-speed cranes. Anti-sway control of suspended loads under cranes has been widely studied, and input shapers have been found as powerful tools. Whereas typical input shapers require variable-speed control for cranes, unity-magnitude (UM) shaper can be applied to fixed-speed cranes. However, UM shaper introduces a start-up delay and over-travel, and thus might not be user-friendly if applied to human-operated cranes. In this work, much simpler anti-sway algorithm for fixed-speed cranes with non-damped oscillations is implemented and evaluated in terms of its robustness. The algorithm is based on the conventional zero-vibration (ZV) shaper, and consists of two sub methods. In the first sub method, the command from an operator is subdivided into a pulse train, which is then fed to ZV shaper. Resulting shaped command is a sum of the original command and one short pulse to suppress the residual oscillation, which is called suppression pulse. Although the command cannot suppress sway during transportation, the crane operated based on the command does not cause start-up delay. On the other hand, the command creates over-travel due to the suppression pulse. To eliminate the over-travel, the second sub method adds a rewind pulse, which is also fed to ZV shaper before being added. The resulting total command exhibits no start-up delay and no over-travel. Experiments using a miniature experimental crane verified the suppression of the residual oscillation, as well as no start-up delay and no over-travel. The paper analyzes its sensitivity against the modeling error. The analyses show that the method is more sensitive to the modeling error when the operation command has a longer duration. Therefore, the algorithm would be effective for cranes with a short-traveling time and/or a long oscillation period.