Characteristics of farm field profiles as sources of tractor vibration

To evaluate farm field profiles as sources of tractor vibration, profiles of meadows, roads and rough terrains were measured and analyzed. A slope angle measuring apparatus with a vertical gyroscope was made to measure profiles using the slope integration method. Periodic uneveness was not found in the measured profiles: therefore it may be assumed that profiles of farm fields, except plowed fields and fields with furrows, are random and non-periodic. Power spectral densities (0.05–3.0 cycles/m) of measured profiles could be approximated by a straight line on a log-log paper. The mean value of spectral slope (2,3) was steeper than that of the recommended value by ISO/TC108/SC2. However, it is suggested that the classification by ISO may be useful to select the profiles of test tracks for the vibration test of tractors and the durability test of tractors and implements. Then the coherency functions were calculated to investigate the correlation between two parallel tracks spaced for the tread width of tractor (1.5m), and the value of coherency functions were small beyond 0.2 cycles/m of spatial frequency. Therefore it is surmised that profiles of paths of tractor wheels are independent.