Effect of Operator Seat Design on Vibration Exposure

Development of an intervention program to reduce whole-body vibration exposure based on occupational and individual determinants among dumper operators

Objectives. Studies related to a systematic approach for intervention design to reduce whole-body vibration (WBV) exposure are scarce. This study presents a systematic approach to identifying, selecting and prioritizing safety interventions to fulfill that research gap. Methods. A total of 130 vibration readings for dumper operators were taken from two surface iron ore mines to identify significant determinants of WBV exposure. Initially, age, weight, seat design, awkward posture, machine's age, load tonnage, dumper speed and haul road condition were hypothesized as determinants. Data were collected through standardized questionnaires and field-based observation. A multivariate statistical approach was applied for the practical use of the intervention program. Results. As some of the hypothesized factors were correlated, exploratory factor analysis (EFA) followed by multiple linear regression (MLR) was used to investigate their association with WBV exposure. As per EFA results, hypothesized factors were clubbed under individual, ergonomics and occupational factors. Occupational and ergonomics factors were found to be significantly associated with WBV exposure through MLR and used to form safety interventions to reduce WBV exposure. Conclusions. Our methodological approach is original in the occupational health research area and can be helpful to tailor the safety interventions for the unit level with minimum effort.

Review on Development of High-Static–Low-Dynamic-Stiffness Seat Cushion Mattress for Vibration Control of Seating Suspension System

This review focuses on studying passive vibration isolation techniques and their applications. Advantages and disadvantages of different vibration isolation techniques will be compared in order to find an innovative method to reduce seating suspension system vibration and improve the ride comfort of vehicles’ drivers. Quasi-zero stiffness (QZS) isolators of high-static–low-dynamic stiffness are found to have good application prospects in low-frequency vibration isolation. In order to improve the isolation performance of the seating suspension system, a specially made seat cushion will be studied where a quasi-zero stiffness (QZS) isolator such as a double-diamond isolator is selected as one of the cells/units/elements of the seat cushion mattress. The double-diamond isolator structure does not represent the whole seating suspension system. The transmissibility ratio of the double-diamond isolator is evaluated by analytical and simulation models and compared to that of a conventional linear spring isolator. Although the performance of the passive vibration isolation/control system is usually worse than that of the active or semi-active control system, the cost of the passive vibration isolation/control system is lower than that of the active and semi-active control system, and the relative simplicity of adding a vibration isolation cushion mattress in an existing passive seating suspension system makes it low in cost, easy to implement, and more attractive than the active and semi-active vibration control systems.

Review on Seat Suspension System Technology Development

This review will focus on the necessity for developing seat vibration control systems as a part of manufacturers’ investigation into finding innovative methods to increase the comfort and safety of the vehicles’ drivers. Operators of either on-road or off-road vehicles are regularly subjected to an extended variety of various vibration levels, especially at low frequencies. Considering that exposure to such vibration in long term has some damaging effects on driver’s health, many comprehensive investigations have been carried out and researchers have proposed several measures for estimating discomfort and the suitability of various vehicles’ seats such as those of trucks, cars and agricultural vehicles in operating condition. Active, passive and semi-active suspension systems are employed in vehicle seats to alleviate the harmful and damaging effects due to the transmitted vibration to the human body. In order to improve riding comfort, the operator’s body displacement and acceleration must be reduced. According to the research, active suspension control systems are the best choice to reduce the transmitted vibration to the drivers’ body and provide the best ride comfort in comparison with passive and semi-active systems.

From the seat to the system: Re-designing a tram drivers' workstation combining technical and contextual aspects

Through the detailed account of a design case-study, the paper aims to demonstrate how the activity-oriented approach promotes a systems perspective in ergonomics interventions. Specifically, by presenting an activity-oriented re-design of a tram drivers' workstation, it is shown: (i) how technical and contextual aspects were jointly considered, (ii) how their combination affects workers' activity in a non-trivial manner, and (iii) how this system level view helped generate feasible and sustainable design solutions. First, the activity-oriented theoretical lens is briefly presented, followed by the analysis of the tram driving activity, emphasizing on drivers' efforts to compensate for the original work-system design flaws. Next, key elements of the re-design process are presented, through a concept map, combining technical and contextual aspects, coupled with an account of stakeholder debates and resolution processes. The paper ends with a discussion on the lessons learned, concerning the adopted approach for design interventions in real work situations.

The influence of seat backrest angle on perceived discomfort during exposure to vertical whole-body vibration

National and International Standards (e.g. BS 6841 and ISO 2631-1) provide methodologies for the measurement and assessment of whole-body vibration in terms of comfort and health. The EU Physical Agents (Vibration) Directive (PAVD) provides criteria by which vibration magnitudes can be assessed. However, these standards only consider upright seated (90°) and recumbent (0°) backrest angles, and do not provide guidance for semi-recumbent postures. This article reports an experimental programme that investigated the effects of backrest angle on comfort during vertical whole-body vibration. The series of experiments showed that a relationship exists between seat backrest angle, whole-body vibration frequency and perceived levels of discomfort. The recumbent position (0°) was the most uncomfortable and the semi-recumbent positions of 67.5° and 45° were the least uncomfortable. A new set of frequency weighting curves are proposed which use the same topology as the existing BS and ISO standards. These curves could be applied to those exposed to whole-body vibration in semi-recumbent postures to augment the existing standardised methods.

PRACTITIONER SUMMARY

Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This article reports new experimental data systematically investigating the effect of backrest angle on discomfort experienced. It demonstrates that most discomfort is caused in a recumbent posture and that least was caused in a semi-recumbent posture.

Predictors of whole-body vibration exposure experienced by highway transport truck operators

Whole-body-vibration (WBV) exposure levels experienced by transport truck operators were investigated to determine whether operator's exposure exceeded the 1997 International Standards Organization (ISO) 2631-1 WBV guidelines. A second purpose of the study was to determine which truck characteristics predicted the levels of WBV exposures experienced. The predictor variables selected based on previous literature and our transportation consultant group included road condition, truck type, driver experience, truck mileage and seat type. Tests were conducted on four major highways with 5 min random samples taken every 30 min of travel at speeds greater than or equal to 80 km/h (i.e. highway driving). Results indicated operators were not on average at increased risk of adverse health effects from daily exposures when compared to the ISO WBV guidelines. Significant regression models predicting the frequency-weighted RMS accelerations for the x (F((5,97)) = 8.63, p < 0.01), y (F((5,97)) = 7.74, p < 0.01), z (F((5,61)) = 9.83, p < 0.01) axes and the vector sum of the orthogonal axes (F((5,61)) = 13.89, p < 0.01) were observed. Road condition was a significant predictor (p < 0.01) of the frequency-weighted RMS accelerations for all three axes and the vector sum of the axes, as was truck type (p < 0.01) for the z-axis and vector sum. Future research should explore the effects of seasonal driving, larger vehicle age differences, greater variety of seating and suspension systems and team driving situations.