LABORATORY TESTING OF OPERATOR SEAT VIBRATION WITH 37 SUBJECTS - CRITICAL COMMENT ON ISO DIS-7096/

The operators of earth moving machinery are often exposed to a low fre quency vibration environment caused by the movement of vehicles over u neven ground and the task carried out. The seat constitutes the last s tate of suspension before the driver. The efficiency of attenuation un der consideration of the best design practice today is the basis for t he revision of ISO 7096 for the testing seats for earth moving machine ry. This standard requires the participation of two subjects with diff erent body masses (52-55 kg; 98-103 kg). The aim of the study was to i nvestigate (1) the extent and the influence of individual variability and posture change on the result of seat tests, and (2) the possibilit y of deducing representative results for the user population. 37 male subjects took part in the experimental investigations. They were expos ed in three postures for 67 s to three acceleration signals in a verti cal direction corresponding to the spectral classes (EM2, EM5, EM6) in ISO/DIS 7096 on two commercial suspension seats. The vertical acceler ations were measured at the seat basis and at the interface between se at cushion and subject. The results of the analysis of variance show a significant influence of exposure, type of seat, and interactions exp osure-by-posture, exposure-by-type of seat, and posture-by-type of sea t on the SEAT factor. Simple and multiple regression analyses were app lied in order to test the predictability of the seat factor (SEAT) by anthropometric variables. The conclusions were drawn that the seat tes ting could be improved by (1) selecting subjects according to the 5th and 95th percentile masses of the population of vehicle or machinery u sers for which the seat is intended (ISO 10326), instead of fixed mass es (ISO 7096), (2) considering other anthropometric parameters for the selection like the body height and body mass supported by the seat, a nd (3) the inclusion of several subjects near the 50th percentile in o rder to assess the variability of the SEAT factor. (C) 1998 Academic P ress.