Vibration Problems in Lift and Escalator Systems: Analysis Techniques and Mitigation Strategies

The operation of lift and escalator installations is often affected by vibrations and vibroacoustic noise. This leads to poor ride quality and a high level of dynamic stresses which may result in damage to the installation. Thus, a good understanding of vibration phenomena occurring in lifts and escalator systems is essential. Lift and escalator systems employ components rotating and translating at speed. Those include elastic tension members such as long ropes, cables, chains and belts. Due to their flexibility and loading conditions they are susceptible to vibration and their dynamic characteristics such as stiffness, mass and damping are time-varying. Thus, the analyst and the designer should be aware that the natural frequencies of a lift and escalator installation change with the time and speed of the transport motion. In lift systems the sources of excitation include the inertial load due to the system acceleration/deceleration profile; periodic excitation caused by the host building structure sway; excitation at the sheave from the drive machine; excitation at the car due to the car-guide rail interaction and aerodynamic effects. Vibration (and noise) in chain-driven escalator installations are often caused by the discrete nature of the chain links and their interactions with the sprocket. The dynamic loads produced by impact between the engaging roller and sprocket surface combined with polygonal action lead to excessive transverse vibrations of the chain. This in turn results in excessive friction wear which reduces the safe service life of the installation. The issues relevant to the vibration theory, modelling, testing and analysis of the dynamic response of lift and escalator systems are addressed in the paper. Then, passive, semi-active and active strategies to minimize the effects of adverse dynamic response of the system are discussed, so that the installation can operate under these conditions without alarm.