Dynamics and performance of clock pendulums

TL;DR

This paper presents a detailed analysis of driven, damped pendulums used in clocks, deriving simplified equations for long-term behavior to improve understanding and simulation of clock accuracy under various disturbances.

Contribution

It introduces first-order ODEs for pendulum amplitude and phase that enable fast long-term simulations, accounting for various errors and disturbances in clock pendulums.

Findings

Equations accurately describe pendulum dynamics over long timescales.

Stationary rate depends on driving torque and friction.

Pendulum reacts predictably to sudden torque changes and noise.

Abstract

We analyze the dynamics of a driven, damped pendulum as used in mechanical clocks. We derive equations for the amplitude and phase of the oscillation, on time scales longer than the pendulum period. The equations are first order ODEs and permit fast simulations of the joint effects of circular and escapement errors, friction, and other disturbances for long times. The equations contain two averages of the driving torque over a period, so that the results are not very sensitive to the fine structure of the driving. We adopt a constant-torque escapement and study the stationary pendulum rate as a function of driving torque and friction. We also study the reaction of the pendulum to a sudden change in the driving torque, and to stationary noisy driving. The equations for the amplitude and phase are shown to describe the pendulum dynamics quite well on time scales of one period and longer. Our emphasis is on a clear exposition of the physics.