Procedure for the reduction of the effect of transient whole body vibrations

Abstract: There is a growing interest in the topic areas of increased vibration comfort and reduced vibration levels in work vehicles. Legislation, health costs and demands for increased competitiveness are all important motivating factors in this growing interest. This Doctoral thesis, based on four papers, is about Whole Body Vibration and focuses on subject responses to transient vibrations attributable to vibration discomfort. Paper I focuses on developing a model that predicts subjective response from overall discomfort and perceived motion during forklift operation. The first objective of the study was to find the effect of various driving conditions on perceived motion and measured vibration. The second objective was to analyze the frequency dependence for each degree of freedom for subjective responses. Tall drivers perceived reduced motion more than did short drivers. In the case of individual results, the relationship between maximum transient vibration value based on the z-direction on the seat and pitch vibrations, and judgments of perceived motion were r=0.63. A perception model based on vibration accelerations in 1/3-octave bands of pitch vibrations and the background variable “body length” gave the best result (r=0.68). Paper II focuses on evaluating the effect of two seat designs in reducing the subjective response from transient vibrations during forklift operations. The seat designs were compared in an experiment based on variations in sitting posture, speed and type of obstacle. The comparison was done by means of assessment of discomfort and perceived motion, and vibration measurement. Results showed that a sliding seat is superior in attenuating vibrations that contain transient vibration in a horizontal direction. The sliding seat was perceived to give less overall discomfort and low back discomfort compared to a fixed seat. Paper III investigates vibration discomfort in a sports utility vehicle (SUV). Sought was to evaluate if and how a vibration exposure and a pause affect perceived vibration discomfort when exposed to a transient vibration. The vibration exposure of slightly uncomfortable vibration levels during 45 minutes did have a significant effect on the assessed vibration discomfort. In Paper IV a methodology to reduce the effect of Whole-Body Vibrations (WBV) on subjects during simulated forklift operations was studied. Two experiments were performed: computer modelling of a forklift and platform simulation. The methodology to reduce the effect from WBV was validated and found to give significant improvements of vibration discomfort. The papers demonstrate that it is possible to develop interventions that reduce perceptions of vibration discomfort. Design strategies such as changes in seat and cab suspension design and an improved understanding of operating condition assessment were identified as being effective in the amelioration of the effect of vibration on operators.