Human response to vibration from earthmoving machines.

The study was concerned with the low frequency vibration generated by wheeled earth moving machines and the consequent discomfort or fatigue risks for the drivers. For these machines the vertical, 'Z', axis was established as the direction of vibration propogation presenting greatest potential risk. The principal reference was IS02631:1978(E) and acceleration levels were measured at frequencies up to 100 Hertz for analysis and comparison. A proposed 'comfort factor' investigation was omitted after the hypothesis was found to require a different methodology and more detailed measurement. Vibrations were recorded from a Landrover and three JCB 3C excavator-loaders, courtesy of JCB Research Ltd. Subsequent analysis showed that excessive acceleration levels, at low frequencies, were received at the driver's seat and that these frequencies also appeared in cab and axle vibrations. Thus the identification of the vibration source became an important aim of the study. The siting of the driver's seat above the drive wheels axle and the absence of axle springing/damping focussed attention onto the tyred wheel. A typical drive wheel was supported in a test/frame and its response to vibration measured. Free vertical movement of the axle was provided by a cantilever arrangement designed not to influence the low frequency response anticipated from the wheel. Finally, a survey of drivers was completed to obtain their subjective assessment of vibration received. Analysis and cross correlation of measured and survey data confirm that discomfort and fatigue will be experienced by the drivers of these machines. The study also provided evidence that the large pneumatic tyres are the sources of the low frequency vibration.