The role of seat suspension in whole-body vibration affecting skidding tractor operators

In mechanised forest operations, whole-body vibration may have considerable influence on machine productivity and on the health of the operator. There is at present in Turkey the potential to exceed the specified limits of international standards for whole-body vibration transmitted to operators during harvesting and skidding operations. The main objective of this study was to compare the effects of seat suspension on the whole-body vibration transmitted to the operators of skidding tractors. Three types of seats (without springs, with couple springs and with four springs) and three different skidding tractors that are commonly used in forestry in Turkey (Ford, International, and Leyland) were selected. Whole-body vibration was analysed at the seat-operator interface on skidding tractors using a tri-axial accelerometer under similar representative working conditions. In the study, the effectiveness of the seat suspension on the transmission of whole-body vibration through the tractor's seat was determined. The highest total acceleration was measured in the seat without springs (1.51 ms(-2)), while the lowest total acceleration was measured in the new seat with four springs (0.76 ms(-2)). The operator of a tractor having a seat without springs is able to work without damage up to 4 hours and 38 minutes per day within the hazard limit (1.15 ms(-2)). On the other hand, the operator of a tractor with a four-spring seat can work 18 hours and 20 minutes in a day within the hazard limit. Statistically significant differences were found between vibration values of the three different seat types using the analysis of variance. According to multiple comparison tests on means, the seats with couple (0.96 ms(-2)) and four springs (0.76 ms(-2)) were in the same group, while the old-style seat without springs (1.30 ms(-2)) was in a different group for total whole-body vibration. In addition to vertical z-axes, the vibration acceleration obtained from the new seat with four springs was significantly lower than the others for the horizontal x-axes. The old-style tractor seat without springs needs to be replaced in order to reduce horizontal-and vertical-direction vibrations. Since the tractor seat with four springs is economical and allows a longer period of work time in a day, the use of high-cost seats with pneumatic or air-suspension systems in skidding operations is not essential