Abstract
The dynamics of a swinging payload suspended from a stationary crane, an unwanted phenomenon on a construction site, can be described as a simple pendulum. However, an experienced crane operator can deliver a swinging payload and have it stop dead on target in a finite amount of time by carefully modulating the speed of the trolley. Generally, a series of precisely timed stop and go movements of the trolley are implemented to damp out the kinetic energy of the simple harmonic oscillator. Here, this mysterious crane operator's trick will be revealed and ultimately generalized to capture the case where the load is initially swinging. Finally, this modus operandi is applied to a torsion balance used to measure G, the universal gravitational constant responsible for the swinging of the crane's payload in the first place.
Highlights
Many engineers have developed robust control algorithms for the automation of industrial cranes to solve the problem of damping the swinging motion of a suspended load
The authors combine their experience of driving overhead cranes (SS, LC) with their love for physics to unveil the principles behind one of the tricks used by crane operators
This technique is applied to a torsion pendulum physics experiment at the National Institute of Standards and Technology (NIST) for measuring the Newtonian constant of gravitation G, showing the ubiquity of simple harmonic motion, ranging from construction sites to the modern laboratory
Summary
Many engineers have developed robust control algorithms for the automation of industrial cranes to solve the problem of damping the swinging motion of a suspended load. Still, few have analyzed the capabilities of the most classic controller—the human crane operator. The authors combine their experience of driving overhead cranes (SS, LC) with their love for physics (all authors) to unveil the principles behind one of the tricks used by crane operators This trick consists of two stop-and-go motions of the trolley. These can damp out the undesirable swinging motion of the pendulum so that it stops dead on target in a finite amount of time.
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