Project Overview
The twist control project addresses a critical challenge in crane operations—payload twist. In crane systems where a payload is suspended by a single looping cable, unwanted twist can lead to safety hazards and reduced operational efficiency. Our objective was to design and implement a control strategy that actively damps the twist using only the existing hoisting hardware, thereby eliminating the need for additional, costly equipment.
Project Objectives & Approach
The main objectives of the project were to:
- Develop a simplified dynamic model of the crane system focusing on payload twist behavior.
- Design a feedback controller that uses hoist acceleration to dampen twist oscillations.
- Maintain precise regulation of the cable length to ensure stable crane operation.
To achieve these objectives, the project team derived a model in which the payload twist dynamics were represented as a nonlinear mass-spring system. Key assumptions were made to simplify the model while retaining its core features. Based on this model, a proportional-derivative (PD) controller, enhanced with an adaptive damping term, was developed to counteract twist motion actively.
Experimental Setup & Results
The control system was implemented on a small-scale tower crane setup. The experimental tests involved varying parameters such as the cable length, the initial twist angle of the payload, and the presence of payload swing. The main performance metric was the 75% settling time—defined as the period required for the twist amplitude to reduce to 25% of its initial value.
In one of the key configurations, the project achieved a dramatic reduction in settling time, with the controller decreasing the time from 183 seconds down to 27 seconds—an 85% improvement. On average, the introduction of the controller across various trials resulted in settling time reductions ranging from 66% to 73%.
Two settling time plots from the project illustrate these performance improvements:
Conclusion & Future Work
The project successfully demonstrated that it is possible to actively control payload twist by leveraging the existing hoisting mechanism. The innovative control strategy effectively damped twist oscillations and maintained accurate cable length regulation, leading to significantly enhanced operational safety and efficiency.
Future work will focus on further refining the controller to handle additional dynamic effects, such as complex payload swing behaviors, and on scaling the approach for larger crane systems.
Acknowledgements
The project was supported by the Sarah Pantip Wong Family through the Crane Safety Research Center
at Georgia Tech.