Influence of forest machine function on operator exposure to whole-body vibration in a cut-to-length timber harvester

The influence of machine function (tree felling and processing, and machine movement over the terrain) on operator exposure to whole-body vibration in a cut-to-length (CTL) timber harvester was evaluated. Vibrations were measured on the seat and the cabin chassis in three orthogonal (x, y, z) axes for the tree felling and processing, and during motion on a test track. It was found that the level of vibration transmitted to the operator during felling and processing was mainly affected by the tree size (diameter). For tree diameter at breast height (dbh) range of 0.25-0.35 m that was investigated, the vertical (z-axis) vibration component during processing increased by up to 300%, and increased by 50% during felling. However, the associated vibration levels were not sufficient to pose any serious health risks to the operator for an exposure limit of 8 h. Vibration at the operator seat and cabin chassis was predominant in the lateral (y-axis) and vertical (z-axis) respectively, during vehicle motion over the standard test track. Vibration peaks of approximately 0.20 and 0.17 ms(-2) occurred at 5 and 3.2 Hz respectively.     

Influence of tyre inflation pressure on whole-body vibrations transmitted to the operator in a cut-to-length timber harvester

The influence of tyre inflation pressure on whole-body vibrations transmitted to the operator during the movement of a cut-to-length timber harvester was evaluated. Vibration measurements were taken in three orthogonal (x, y, z) axes at tyre pressure settings of 138, 345 and 414 kPa. Vibration was predominant in the vertical (z) direction with the peak rms acceleration value for the operator seat (0.281 ms(-2)) occurring at approximately 3.2 Hz.The corresponding peak value for the operator cabin chassis was 0.425 m s(-2) at 4 Hz.At 414 kPa, there was potential health risk on the operator for exposures above 8h duration. The vibration total values recorded for the operator seat at the maximum tyre inflation pressure setting were classed as "fairly uncomfortable" (ISO standard 2631-1), and vertical seat vibration transmissibility was highest between 4 and 8 Hz at the 345 kPa tyre pressure setting. The recorded values of WBV were significantly reduced by a reduction in tyre inflation pressure which may therefore be used to moderate the magnitude of WBV on wheeled timber harvesters.     

Experimental analysis of occupational whole-body vibration exposure of agricultural tractor with large square baler

This study investigates longitudinal whole-body vibration in agricultural tractors powering a large square baler. The aim is to test the hypothesis that four-wheel drive has an influence on the longitudinal dynamic response. A number of experimental measurements are carried out on a specific vehicle combination driving uphill and downhill. The whole-body vibration exposure is measured at the operator seat under different conditions.The statistic results show a significant difference on the whole-body vibration exposure depending on operating conditions. Driving uphill and downhill with four-wheel drive activated showed the highest difference with increased vibration level at downhill driving.The results indicate that four-wheel drive influences the longitudinal dynamics and hence the whole-body vibration exposure on tractors with large square balers.Relevance to industryThe findings of this work are highly relevant to the manufacturers of agricultural tractors and machinery as well advisers within occupational health. The paper demonstrates potential in reducing damaging vibrations by simple manual or automatic control of four-wheel drive.     

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.     

Joint evaluation of recovery and performance of a COTS DBMS in the presence of operator faults

A major cause of failures in large database management systems (DBMS) is operator/administrator faults. Although most of the complex DBMS available today have comprehensive recovery mechanisms, the effectiveness of these mechanisms is difficult to characterize. On the other hand, the tuning of a large database is very complex and database administrators tend to concentrate on performance tuning and disregard the recovery mechanisms. Above all, database administrators seldom have feedback on how good a given configuration is concerning recovery. This paper proposes an experimental approach to characterize both the performance and the recoverability of DBMS. Our approach is presented through a concrete example of benchmarking the performance and recovery of an Oracle DBMS running the standard TPC-C benchmark, extended to include two new elements: a faultload based on operator faults and measures related to recoverability. A classification of operator/administrator faults in DBMS is proposed. A set of tools have been designed and built to reproduce operator faults in an Oracle 8i DBMS, using exactly the same means used in the field by the real database administrator. This experimental approach is generic (i.e., can be applied to any DBMS) and is fully automatic. The paper ends with the discussion of the results and the proposal of guidelines to help database administrators in finding the balance between performance and recovery tuning.     

The role of whole-body vibration in back pain: A cross-sectional study with agricultural pilots

ObjectiveA cross-sectional study was conducted to investigate the role of whole-body vibration as a risk factor for spinal musculoskeletal symptoms among agricultural pilots.MethodThe study was conducted in two stages that included measuring the pilots’ exposure to whole-body vibration during the flight procedures and applying a self-administered questionnaire about musculoskeletal symptoms of the spine.ResultsNone of the four aircraft texted exposed the pilot above the Exposure Limit Value (ELV) established by the standards. However, in a few specific situations, two of them exceeded the Exposure Action Value (EAV). About 62% of the pilots who operated these aircraft reported some musculoskeletal symptoms of the spine in the last few 12 months.ConclusionUsing the data from this study, it was possible to calculate the odds ratio of the agricultural pilot suffering low back pain, based on eight personal and work-related factors.Relevance for the industryBased on the results of the present study, it was possible to define strategies to reduce whole-body exposure in agricultural aircraft and, consequently, improve the pilots’ health. Strategies included management of the exposure and aircraft improvement.     

Performance of a complex manual control task during exposure to vertical whole-body vibration between 0·5 and 5·0 Hz

An experiment is described in which seated subjects performed first-order pursuit tracking with a simultaneous discrete task; performance with the discrete task was dependent on performance of the continuous task. Vertical, z-axis, whole-body sinusoidal vibration was presented at frequencies from 0·5 to 5·0Hz at an acceleration magnitude of 2·0 ms^?2 r.m.s. in three separate sessions. In the first session, inter-subject and intra-subject variability masked any disruption caused by the vibration. After further training, all vibration frequencies disrupted performance of the continuous task. Disruption was independent of vibration frequency below 3·15Hz and increased at 4·0 and 5·0Hz. A visual mechanism was assumed to account for the increased disruption at these higher frequencies. Mechanisms which may have been responsible for the disruption below 3·15 Hz are discussed. Effects of vibration on the discrete task were attributable to disruption in performance of the continuous task. The results illustrate the importance of adequately training subjects prior to investigating vibration effects.     

Exposure to and effects of glare from high mast lighting on workers at a timber terminal

High mast floodlighting at outdoor workplaces has economic advantages but suffers from shortcomings such as glare. This study was made to collect and evaluate data from a situation with glare from a physical and occupational health standpoint. When unloading timber, the worker's gaze is frequently directed upward, whereas conventional glare indexes for luminaires assume the gaze is diagonally downwards. It was found that reduced visual acuity could cause difficulty in normal working routines.     

Evaluation of whole-body vibration exposure experienced by operators of a compact wheel loader according to ISO 2631-1:1997 and ISO 2631-5:2004

Limited studies were carried out to evaluate the whole-body vibration (WBV) exposure experienced by operators of compact wheel loaders (CWLs) according to ISO 2631-1:1997. No study was carried out according to ISO 2631-5:2004. Therefore, evaluation of the WBV exposure using these two standards was carried out and the results were compared in this study. Tri-axial accelerations were measured at the seat/operator interface on a medium-sized CWL. The vibration measurements were carried out in ten different operations, such as the V-cycle and the driving over different road surfaces. In order to represent the daily work of the CWL, seven scenarios were proposed. These scenarios are comprised of V-cycle and driving over different distances. The evaluation result according to ISO 2631-1:1997 showed that the permitted daily exposure durations of six scenarios estimated using the vibration dose value (VDV) method did not exceed 8 h. For the pure V-cycle and the combination of V-cycle and slow driving, the permitted daily exposure durations estimated according to ISO 2631-1:1997 were shorter than those estimated according to ISO 2631-5:2004. However, for the combination of V-cycle and fast driving, the permitted daily exposure durations estimated according to ISO 2631-1:1997 were longer than those estimated according to ISO 2631-5:2004.Relevance to industryThis study evaluated the effect of WBV arising from a CWL on human health according to ISO 2631-1:1997 and ISO 2631-5:2004. Evaluation results show that boundaries of the health guidance caution zone in ISO 2631-5:2004 are higher than those in ISO 2631-1:1997.     

Predicting the health risks related to whole-body vibration and shock: a comparison of alternative assessment methods for high-acceleration events in vehicles

In this paper, alternative assessment methods for whole-body vibration and shocks are compared by means of 70 vibration samples measured from 13 work vehicles, deliberately selected to represent periods containing shocks. Five methodologies (ISO 2631-1:1997, BS 6841:1987, ISO 2631-5:2004, DIN SPEC 45697:2012 and one specified by Gunston [2011], ‘G-method’) were applied to the vibration samples. In order to compare different evaluation metrics, limiting exposures were determined by calculating times to reach the upper limit thresholds given in the methods. Over 10-fold shorter times to exposure thresholds were obtained for the tri-axial VDV (BS 6841) than for the dominant r.m.s. (ISO 2631-1) when exposures were of high magnitude or contained substantial shocks. Under these exposure conditions, the sixth power approaches (ISO 2631-5, DIN SPEC, G-method) are more stringent than a fourth power VDV method. The r.m.s. method may lead to misleading outcomes especially if a lengthy measurement includes a small number of severe impacts. In conclusion, methodologies produce different evaluations of the vibration severity depending on the exposure characteristics, and the correct method must be selected.     

The performance of foliage mass and crown radius models in forming the input of a forest reflectance model: A test on forest growth sample plots and Landsat 7 ETM+ images

Several published foliage mass and crown radius regression models were tested on the preparation of the input for the reflectance model of Kuusk and Nilson [Kuusk, A. and Nilson, T. (2000), A directional multispectral forest reflectance model. Remote Sensing of Environment, 72(2):244–252.] for 246 forest growth sample plots in Estonia. In each test, foliage mass and crown radius for trees in the sample plots were predicted with a particular pair of allometric regression models. The forest reflectance model was then run using the estimated foliage mass and crown radius values. Reflectance factors were simulated and compared with the reflectance values obtained from three atmospherically corrected Landsat 7 Enhanced Thematic Mapper (ETM+) scenes. The statistics of linear regression between the simulated and measured reflectance factors were used to assess the performance of foliage and crown radius models. The hypothesis was that the best allometric regression models should provide the best fit in reflectance. The strongest correlation between the simulated and measured reflectance factors was found in the short-wave infrared band (ETM + 5) for all the images. The highest R² = 0.71 was observed in Picea abies dominated stands. No excellent combination of foliage mass and crown radius functions was found, but the ranking based on determination coefficients showed that some linear crown radius models are not applicable to our data. Processing of raster images, reflectance measurement for small sample plots, usage of tree-species-specific fixed parameters (specific leaf area, etc.), and the ignored influence of phenology introduced additional variation into the relationships between simulated and measured reflectance factors. Further studies are needed, but these preliminary results demonstrate that the proposed method could serve as an effective way of testing the performance of foliage mass and canopy cover regressions.     

Evaluation of thermal and moisture management properties on knitted fabrics and comparison with a physiological model in warm conditions

This study reports on an experimental investigation of physical properties on the textile thermal comfort. Textile properties, such as thickness, relative porosity, air permeability, moisture regain, thermal conductivity, drying time and water-vapour transmission rate have been considered and correlated to the thermal and vapour resistance, permeability index, thermal effusivity and moisture management capability in order to determine the overall comfort performance of underwear fabrics. The results suggested that the fibre type, together with moisture regain and knitted structure characteristics appeared to affect some comfort-related properties of the fabrics. Additionally, thermal sensations, temperature and skin wetness predicted by Caseto^® software for three distinct activity levels were investigated. Results show that the data obtained from this model in transient state are correlated to the thermal conductivity for the temperature and to Ret, moisture regain and drying time for the skin wetness. This provides potential information to determine the end uses of these fabrics according to the selected activity level.     

The role of the New Zealand forest industry injury surveillance system in a strategic ergonomics,safety and health research programme

Forestry is among the most hazardous of all industry sectors internationally. In New Zealand, highest work-related morbidity and mortality incidence rates are found in the logging sector. The New Zealand Forest Industry Accident Reporting Scheme (ARS) is a forestry injury surveillance system maintained by the Centre for Human Factors and Ergonomics (COHFE). The paper highlights the pivotal role of an industry-wide injury surveillance system in an industry-specific strategic research programme, giving examples of the use of ARS data in identification of priority areas for ergonomics, safety and health research attention, for safety awareness feedback to the industry, and in the evaluation of injury countermeasures. An analysis of injury patterns and trends for one high-risk forestry operation (skid work) is presented to illustrate both the capabilities and limitations of the ARS in its present stage of development.     

The influence of different electronic maps and displays on performance and operator state in a geographic orientation task

Mobile electronic displays for geographic orientation and navigation are used increasingly in various civil and military domains. But it is still unclear which displays and kinds of map presentation suit best for specific purposes. In the present experiment, a head-mounted display (HMD) and a display from a personal digital assistant (PDA) were compared in a simulated geographic orientation task in an urban environment. Furthermore, the effect of three kinds of map presentation (egocentric, geocentric and geocentric with colour cues) was analysed. The simulated orientation task was projected on a screen and participants controlled their locomotion within the urban area by means of a joystick. Task completion time, peripheral attention, workload, fatigue and simulator sickness were registered as dependent variables. In comparison to the geocentric map the egocentric map showed a significant shorter task completion time and the geocentric map with colour cues a significant higher peripheral attention. Task completion time of the HMD and the PDA did not differ significantly. However, peripheral attention and most indices of workload, fatigue and simulator sickness were significantly better for the PDA. Therefore, the results recommend to apply PDAs and egocentric maps for comparable orientation tasks.     

Fault detection and diagnosis approach based on nonlinear parity equations and its application to leakages and blockages in the drying section of a board machine

This study aims at providing a fault detection and diagnosis (FDD) approach based on nonlinear parity equations identified from process data. Process knowledge is used to reduce the process nonlinearity from high to low-dimensional nonlinear functions representing common process devices, such as valves, and incorporating the monotonousness properties of the dependencies between the variables. The fault detection approach considers the obtained process model to be nonlinear parity equations, and fault diagnosis is carried out with the standard structured residual method. The applicability of the approach to complex flow networks controlled by valves is tested on the drying section of an industrial board machine, in which the key problems are leakages and blockages of valves and pipes in the steam–water network. Nonlinear model equations based on the mass balance of different parts of the network are identified and validated. Finally, fault detection and diagnosis algorithms are successfully implemented, tested, and reported.     

Setting due dates to minimize the total weighted possibilistic mean value of the weighted earliness-tardiness costs on a single machine

In this paper, it is investigated how to sequence jobs with fuzzy processing times and predict their due dates on a single machine such that the total weighted possibilistic mean value of the weighted earliness-tardiness costs is minimized. First, an optimal polynomial time algorithm is put forward for the scheduling problem when there are no precedence constraints among jobs. Moreover, it is shown that if general precedence constraints are involved, the problem is NP-hard. Then, four reduction rules are proposed to simplify the constraints without changing the optimal schedule. Based on these rules, an optimal polynomial time algorithm is proposed when the precedence constraint is a tree or a collection of trees. Finally, a numerical experiment is given.     

Scheduling n jobs on one machine to minimize the maximum lateness with a minimum number of tardy jobs

This study considers the problem of scheduling n jobs, each job having an arrival time, a processing time and a due date, on a single machine with the dual objective of minimizing the maximum lateness subject to obtaining a minimum number of tardy jobs. A simple procedure is introduced to identify two critical jobs from which the maximum lateness is generated for a given sequence. The sequence of jobs between two critical jobs inclusive is called the critical path. On the basis of the critical path, Carlier's binary branching rule is adopted to minimize the maximum lateness. By fixing the position of these two critical jobs for maintaining the minimum maximum lateness, the sequence can further be reordered to reduce the number of tardy jobs. A branch and bound algorithm is presented for this purpose. The algorithm can solve problems with 50 jobs optimally within 5 seconds on a PC Pentium-100.     

Influence of turbulence and atmospheric chemistry on grid size with respect to location in modeling and simulation of photochemical smog formation and transport

In models for photochemical smog formation and transport, mixing is assumed to be instantaneous and consequently the reactions are assumed to be kinetically controlled. In this work, the Damkohler number is calculated to check the validity of this assumption. The results show that this number is above 50, especially near pollution point sources such as the power station stacks, so that the diffusion limits the reactions for such cases. Using the irregular or adaptive grids minimized the Damkohler number and diffusion limitations which indicates that the grids should be finer near the source and coarser in remote regions. Therefore, depending upon the atmospheric conditions and emission sources, one can determine the optimum grid sizes for modeling and simulation of photochemical smog.