Six degree of freedom whole-body vibration during forestry skidder operations

Abstract

Exposure to whole-body vibration (WBV) has been associated with a wide variety of health disorders. While previous work has established that forest machine operators are exposed to high levels of translational WBV, there are no reports which have quantified field levels of rotational vibration; therefore, the purpose of this work was to quantify six degree of freedom (6-DOF) accelerations that forest machine operators are exposed to during routine machine operations as well as to assess potential health risks and determine the effect of various measurement locations (chassis, seat/operator interface (SOI)), driving conditions (driving loaded (DL), driving unloaded (DUL)) and axis ( X, Y, Z and roll, pitch, yaw). Simultaneous measures of 6-DOF acceleration from both the SOI and chassis were determined for seven skidders operating in Northern Ontario boreal forest conditions during the months of June and July 2006. Average running root mean squared (RMS) ISO 2631-1:1997 weighted accelerations were between 0.72 and 1.12 m/s 2 and 0.33 and 0.79 rad/s 2 at the SOI in the translational and rotational axes, respectively. The dominant frequency and the SOI and chassis was determined to be 1 Hz at both at the chassis and SOI while DL and DUL in the X- and Y-axes, and 2 Hz in Z-axis. The acceleration data indicate an uncomfortable/very uncomfortable ride for skidder operators. The acceleration skidder operators are exposed to exceed the upper exposure limit for a 4-h work day as outlined in ISO 2631-1:1997, and are thus likely to incur some health effects. ANOVA procedures revealed significant ( p⩽0.05) differences between weighted RMS accelerations at the dominant frequency and running weighted RMS accelerations for driving condition (DUL>DL), measurement location (SOI >chassis) and axis ( Y> X> Z and roll>pitch>yaw). To our knowledge, this data represents the most comprehensive 6-DOF field data set collected and analyzed to date for any type of forestry vehicle. The results of this study indicate that skidder seats amplify the WBV accelerations occurring at the SOI when compared to corresponding values measured at the chassis. The acceleration values outlined in this study are similar to those published over the past 20 years suggesting that little has changed with respect to the ability of the seat to attenuate harmful vibration and/or the ability and/or willingness of the operator to adjust the seat in order to optimize seat effectiveness. Relevance to industry Quantification provided by this study is useful to forest machine and heavy equipment seat designers. Field profiles developed from this data are being used in 6-DOF robot laboratory studies to assess WBV attenuation capabilities of current and future seat designs and to develop new biodynamic measures of seat effectiveness.