Non-linear energy accumulation buffers

Lift buffers are listed as safety components in Annex IV of EC Directive 96/16/EC on lifts. Requirements for the application and type testing of buffers, including non-linear energy accumulation buffers, are given in EN 81-1. Their function is to limit acceleration levels in the event that either the car or counterweight reaches the ends of the lift well without the normal slowing down having been effective. In this paper, lift car buffering at the bottom of the well is considered. Of the three types of buffers commonly accepted by the main codes, both linear energy accumulation (spring) and energy dissipation (hydraulic type) buffers are readily analysed in relation to the acceleration levels of persons in the lift car and have had requirements for their application in the main codes for a long time. Non-linear energy accumulation (polyurethane or elastomeric) buffers have had requirements in EN 81 for a shorter time commensurate with the time that these types have been in common use. These, since their buffering forces are highly non-linear with buffer compression, make prediction of the behaviour of the lift car under buffering more difficult. This paper is intended to provide a simple model assessing the behaviour of the lift car once it has impacted non-linear energy accumulation buffer(s). This model is used with a number of buffer characteristic curves and with a range of loads and buffer impact speeds, both in the free fall and assuming that the suspension remains intact, to examine the likely behaviour of the lift car after contacting the car buffer(s). A further intention is to critically examine both the average and peak accelerations derived from the model in relation to the requirements in EN 81-1.