Evaluation of commercially available seat suspensions to reduce whole body vibration exposures in mining heavy equipment vehicle operators

Experimental Analysis of Passenger Comfort with Variable Preloaded Rear Springs on a Low-Cylinder Motorcycle

The present study contains an experimental analysis of the vibratory response in a low-cylinder engine motorcycle at varying suspension preloads. Three different speed bumps of varying heights were used to subject the motorcycle to different vibrations. The analysis was carried out in three domains: time, frequency, and time-frequency. A triaxial accelerometer was used to measure the vibrations at the seat of the vehicle. The results indicated that the suspension system became more differentiated as the height of the bumps increased. However, for lower bumps, the action of the three spring preloads studied was quite similar. Quantitatively, only the higher bump showed a significant difference between the set preloads. The spectral distribution revealed that the frequency of interest was below 20 Hz for all the studied cases, which is in the same range of human body natural frequencies. The findings of this research can be utilized to enhance the design of low-cost motorcycles, thereby improving the safety and comfort of their drivers and passengers. This study constitutes a significant step towards developing an affordable system capable of gathering sufficient data to support the creation of evidence-based public health policies and propose new transport industry standards based on field measurements.

Perceived discomfort and neuromuscular fatigue during long-duration real driving with different car seats

INTRODUCTION

Identification of the seat features that could improve driving experience is a main issue for automotive companies.

OBJECTIVE

Long duration real driving sessions were performed to assess the effect of three seats (soft-S1, firm-S2 and suspended-S3) on perceived discomfort and neuromuscular fatigue (NMF).

MATERIALS & METHODS

For each seat, the muscular activity of bilateral Trapezius Descendens (TD), Erector Spinae (ES) and Multifidus (MF) muscles of twenty-one participants was recorded during real driving sessions of 3-hours each lasting approximately 3 hours and following the same itinerary. During each driving session, participants were also regularly asked to self-evaluate their level of whole-body and local discomfort. In addition, an endurance static test (EST) was performed before (ESTpre) and after (ESTpost) each driving session to assess the seat effect on physical capacity.

RESULTS

Whole-body discomfort increased with driving time for all seats, but this increase became significant latter for S3. The highest scores of local discomfort occurred for neck and lower back. Contrary to S1 and S2, the duration of ESTpost was not significantly lower compared to ESTpre with the S3. Interestingly, muscular activity of S1 remained stable throughout the driving task which could be attributed to sustained muscular contraction, while muscular recruitment adjustments occurred for S2 and S3 from 1H00 of driving. This muscular compensation concerns mostly the right side for S2 and S3 but with different profiles. On the left side, the muscular adjustments concern only the MF with S2 and the ES with S3.

CONCLUSION

Overall, our results demonstrated that S3 could be considered as the most suitable seat to delay discomfort and NMF appearance.

Evaluation of vertical and multi-axial suspension seats for reducing vertical-dominant and multi-axial whole body vibration and associated neck and low back joint torque and muscle activity

The primary aim of this laboratory-based human subject study was to evaluate the biomechanical loading associated with mining vehicles' multi-axial whole body vibration (WBV) by comparing joint torque and muscle activity in the neck and low back during three vibration conditions: mining vehicles' multi-axial, on-road vehicles' vertical-dominant, and no vibration. Moreover, the secondary aim was to determine the efficacy of a vertical passive air suspension and a prototype multi-axial active suspension seat in reducing WBV exposures and associated biomechanical loading measures. The peak joint torque and muscle activity in the neck and low back were higher when exposed to multi-axial vibration compared to the vertical-dominant or no vibration condition. When comparing the two suspension seats, there were limited differences in WBV, joint torque, and muscle activity. These results indicate that there is a need to develop more effective engineering controls to lower exposures to multi-axial WBV and related biomechanical loading. Practitioner Summary: This study found that mining vehicles' multi-axial WBV can increase biomechanical loading in the neck and back more so than on-road vehicles' vertical-dominant WBV. While a newly-developed multi-axial active suspension seat slightly reduced the overall WBV exposures, the results indicate that more effective engineering controls should be developed. Abbreviation: APDF: amplitude probability density function; Aw: weighted average vibration; BMI: body mass index; C7: The 7th cervical vertebra; EMG: electromyography; ES: erector spinae; IRB: institutional review board; ISO: International Organization for Standardization; L5/S1: the fifth lumbar vertebra (L5)/the first sacral vertebra(S1); MSDs: musculoskeletal disorders; MVC: maximum voluntary contraction; PSD: power spectral density; RVC: reference voluntary contraction; SCM: sternocleidomastoid; SD: standard deviation; SPL: splenius capitis; TRAP: trapezius; VDV: vibration dose value; WBV: whole body vibration.

Tractor Cab Ergonomics Optimization Based on the Simplified Model of Upper Limb from the Perspective of Public Health

The study of tractor ergonomics is both an essential part of public health and a very significant part of the scientific community's focus at the moment. It offers a foundation for the layout design of the tractor cab, making it possible to effectively avoid occupational diseases, minimize the number of safety accidents, and enhance the comfort of operation. Devices are categorized as control rod devices, knob-type devices, and steering wheels according to the various modes of operation of the tractor cab. Steering wheels are also included. The ease of handling of a number of different components was ranked according to how well they performed on the fast evaluation approach for the upper limbs. After that, in accordance with the concept that underpins this evaluation approach, the comfortable range of motion of human upper limb joints is evaluated while undergoing a variety of manipulation modalities. In conjunction with the structure of the human body and the characteristics of its movement, a streamlined point-line structure model of the human upper limb is constructed, with the H-point serving as the reference point. The problem of figuring out how to distribute the control components in the best possible way has been solved, and the optimal distribution range diagram of the steering wheel has been obtained. The ideal height for the distribution of control rod devices is around 300-400 millimeters, whereas the ideal height for the distribution of knob-type devices is approximately 200-500 millimeters. In conclusion, the cab design of the KAT2204 tractor is improved upon thanks to the analysis done in this study, which can be found above. The legitimacy of the research conclusion is confirmed by the fact that the RULA value is lower than 2, which is proved by the fact that the design findings are validated by the Creo Manikin module. The ergonomics of the tractor cab were taken into consideration when using this research approach as a reference.

Dynamic interaction between the human body and the seat during vertical vibration: effect of inclination of the seat pan and the backrest on seat transmissibilities

Seat inclinations at the seat pan and backrest may affect the sitting comfort. This study was designed to quantify the effect of inclination of a seat pan (0°, 10°, and 20°) and backrest (0°, 15°, and 30°), either foamed or rigid, on the transmissibilities measured at the seat pan and backrest. Seat transmissibilities were measured with fifteen subjects exposed to vertical random vibration between 1 and 15 Hz at 0.5 ms^-2 r.m.s. It was found the resonance frequencies in transmissibilities measured at the seat pan and backrest increased with increasing the backrest inclination but were not affected by the seat pan angle. Increasing the foamed backrest inclination increased the peak transmissibilities. Inclination of the rigid seat pan or the rigid backrest reduced the transmissibilities measured at the backrest or the seat pan, respectively. Transmissibilities were more significantly affected by the backrest inclination than the seat pan inclination. Practitioner summary: Seat inclinations may alter the human-seat dynamic interaction and hence the riding discomfort. This study was designed to quantify the effect of inclined seats, either foamed or rigid, on the transmissibilities. It was found the backrest angle affected the transmissibilities more strongly than the seat pan angle.

The effects of a new seat suspension system on whole body vibration exposure and driver low back pain and disability: Results from a randomized controlled trial in truck drivers

Through a randomized controlled trial, we evaluated the effects of an electro-magnetic active seat suspension that reduces exposure of a long-haul truck driver to whole body vibration (WBV) on low back pain (LBP) and disability. Among 276 drivers recruited from six trucking terminals of a major US trucking company, 135 eligible drivers were assigned to either having an Active Seat (Intervention: n = 70) - the BoseRide® electro-magnetic active seat - or Passive Seat (reference: n = 65) - a new version of their current seat (passive air suspension seat) - installed in their truck via block (terminal) randomization. Low back pain (LBP) severity, on a 0-10 scale and the Oswestry LBP Disability Index were collected before and 3-, 6-, 12-, 18-, and 24-months post seat installation. LBP severity and LBP disability scores were significantly lower post seat installation in both groups. At 3 months, LBP severity decreased -1.4 [95% CI: -2.1 to -0.7: n = 46] for drivers in the Active Seat arm, and -1.5 [95% CI: -2.3 to -0.8: n = 41] for drivers in the Passive Seat arm. In a subset of drivers, WBV exposures were collected before and after the seat installation. WBV exposures significantly decreased post seat installation for Active Seat (p < 0.01) but not for Passive Seat (p = 0.15). While the new seat-suspension technology reduced WBV exposures, LBP appeared to be improved by multiple factors. These results were limited by the secondary prevention approach and the longer-term loss to follow up due to large rates of driver turnover typical for the industry.

Theoretical Analysis and Optimization of a Gloved Hand-Arm System

Studies have shown that isolators in the form of antivibration (AV) gloves effectively reduce the transmission of unwanted vibration from vibrating equipment to the human hand. However, as most of these studies are based on experimental or modeling techniques, the level of effectiveness and optimum glove properties for better performance remains unclear. To fill this gap, hand-arm system dynamics with and without gloves are studied analytically in this work. In this work, we use a lumped parameter model of the hand-arm system, with hand-tool interaction modeled as a linear spring-damper system. The resulting governing equations of motion are solved analytically using the method of harmonic balance. Parametric analysis is performed on the biomechanical model of the hand-arm system with and without a glove to identify key design parameters. It is observed that the effect of glove parameters on its performance is not repetitive and changes in the studied different frequency ranges. This observation further motivates us to optimize the glove parameters to minimize the overall transmissibility in different frequency ranges.

The Effects of Whole-Body Vibration Exercise on Anticipatory Delay of Core Muscles in Patients with Nonspecific Low Back Pain

Objective

The objective of this study is to determine the effect of whole-body vibration (WBV) exercise on the anticipatory delay of core muscles in nonspecific low back pain (NSLBP) patients.

Methods

Forty participants with NSLBP were randomly divided into the WBV group and the control group. The sEMG signals of deltoid, erector spines (ES), multifidus (MF), rectus abdominis (RA), and transversus abdominus/internal oblique muscles (TrA/IO) were recorded before and after the intervention in the weight-shifting task. The relative activation time of each muscle was calculated.

Results

In the WBV group, the relative activation time of bilateral MF and bilateral TrA/IO was significantly reduced on shoulder flexion (right MF: P=0.014; left MF: P=0.011; right TrA/IO: P=0.008; left TrA/IO: P=0.026). As for shoulder abduction, except for the left TrA/IO and the left RA, the relative activation time of other muscles was significantly reduced (right ES: P=0.001; left ES: P < 0.001; right MF: P=0.001; left MF: P=0.009; right TrA/IO: P < 0.001; right RA: P=0.001). In the control group, there was no significant difference in the relative activation time of each muscle before and after the intervention (P > 0.05).

Conclusions

WBV exercise can effectively alleviate the anticipatory delay of core muscles in NSLBP patients, but the long-term effects still need further study. This trial is registered with ChiCTR-TRC-13003708.

The effects of different seat suspension types on occupants' physiologic responses and task performance: implications for autonomous and conventional vehicles

This study evaluated whole body vibration (WBV), non-driving task performance, muscle activity, and self-reported discomfort and motion sickness between different seat suspension systems in a simulated vehicle environment. In a repeated-measures laboratory experiment where field-measured 6-degree-of-freedom (6-DOF) passenger vehicle vibration was replicated on a 6-DOF motion platform, we measured WBV, non-driving task (pointing, typing, web-browsing, and reading) performance, low back (erector spinae), shoulders (trapezius) and neck (splenius capitis and sternocleido-mastoid) muscle activity, and self-reported discomfort and motion sickness from three different seats: a vertical (z-axis) active suspension, multi-axial active suspension [vertical (z-axis) + lateral (y-axis)], and a static suspension-less seat (current seat type in all passenger cars). Both the vertical and multi-axial active suspension seats significantly reduced the vertical WBV exposure (p < 0.0001). However, no significant differences were found in non-driving task performance (p > 0.30), muscle activity (p > 0.22), self-reported discomfort (p > 0.07), and motion sickness (p = 0.53) across three different seats. These findings indicate that the active suspension seats may have potential to future reduce the vertical and total WBV exposures, respectively. However, none of the suspension seats demonstrate any significant benefits on the non-driving task performance, muscle activity, self-reported discomfort and motion sickness measures in a simulated vehicle environment.

Preventive action with a population of excavator drivers exposed to whole-body vibration

BACKGROUND:

Whole-body vibration is a major cause of lower back pain among employees, and the medical and preventive care teams of occupational health departments are often confronted with lower back pain problems among machine operators.

OBJECTIVES:

The objectives of this research are to determine the number of excavator drivers exposed to whole-body vibration levels above 0.5m/s², identify other exposure factors that may contribute to back pain, and propose corrective measures.

METHODS:

Vibration measurements were carried out on individual excavator drivers while they were observed carrying out working tasks, after which prevention advice is given. Factors which determine vibration levels are logged on to a database.

RESULTS:

The multivariate analysis of several determining factors shows vibration exposure levels vary depending on the varied work tasks being carried out.

CONCLUSION:

This study identifies exposed employees among excavator operators. For each workstation, the determining factors that could explain the high exposures to vibrations are identified. This work shows the important role of tasks on exposure levels. A better adaptation of the tools used to carry out work tasks would allow a decrease in the vibration level of this type of machine.

Postural balance effects from exposure to multi-axial whole-body vibration in mining vehicle operation

Twenty participants (18 males and 2 females) completed postural stability assessments before and after 4-h exposure to whole body vibration (WBV) in four experimental conditions: (a) vertical-dominant WBV with vertical passive air suspension, (b) multi-axial WBV with vertical passive air suspension, (c) multi-axial WBV with multi-axial active suspension, and (d) no WBV condition. Center of pressure (COP)-based postural sway measures significantly increased following multi-axial WBV exposure. Increase in COP velocity and displacement following multi-axial WBV was significantly higher than the increase in all the other exposure conditions. However, no significant differences between the WBV conditions were observed in functional limits of stability and anticipatory postural adjustments. While our results show standing balance to be impaired following the multi-axial WBV exposure of off-road mining vehicles, dynamic stability across a broader range of conditions needs to be understood to causally link postural stability decrements to increased fall-risks associated with off-road vehicle operators.

Musculoskeletal Symptoms among Stone, Sand and Gravel Mine Workers and Associations with Sociodemographic and Job-Related Factors

Stone, sand and gravel mining (SSGM) constitutes the vast majority of mining operations in the United States. Despite musculoskeletal disorders being one of the most common occupational health problems across several industries, limited research has examined the extent of reported musculoskeletal symptoms or disorders among actively employed SSGM workers. To address this knowledge gap, cross sectional data were collected from 459 SSGM workers in the Midwestern United States to determine the prevalence of musculoskeletal symptoms. Sociodemographic and job-related factors were examined to identify possible risk factors in SSGM. Musculoskeletal symptoms of the low back (57%), neck (38%), shoulder (38%) and knee (39%) were highly prevalent among SSGM employees. The results, among other findings, showed that working more than 60 h a week increased the likelihood of musculoskeletal symptoms at the low back (OR: 4.7 95% CI: 1.9–11.5), neck (OR: 5.1, 95% CI: 2.2–11.8) and knee (OR: 4.5, 95% CI: 2.0–10.3). Working as a mechanic/maintenance worker increased the likelihood of low back (OR: 2.1, 95% CI: 1.1–4.2) and knee (OR: 2.2, 95% CI: 1.1–4.6) musculoskeletal symptoms. Intervention measures aimed at improving ergonomic hazard identification for various job tasks as well as administrative controls limiting hours worked may help reduce the burden of musculoskeletal problems in the SSGM industry.

Effect of whole-body vibration exposures on physiological stresses: Mining heavy equipment applications

The aim of this study was to employ validated biological markers to quantify the physiologic consequences of exposure to whole-body vibration (WBV) and evaluate the relative impact of mining vehicle operator vibration exposure on physiological responses as compared to vertical-axial dominant WBV. In a laboratory-based study with a repeated-measures design, we played actual field-measured floor vibration profiles into a 6-degree-of-freedom motion platform to create different realistic WBV exposures: 1) vertical-dominant vibration collected from long-haul trucks, 2) multi-axial vibration collected from mining heavy equipment vehicles, and 3) no vibration (control condition). Circulating biomarkers of interest were cortisol and catecholamines (epinephrine and norepinephrine) to assess physiological stress, interleukin-6 (IL-6) and tumor necrosis factor-α (TNFα) to test for inflammation, thiobarbituric acid reactive substances (TBARS) to measure oxidative stress, and myoglobin and plasma creatine kinase to assess muscle damage. We collected blood samples at pre-exposure (0 h), during-exposure (2 and 4 h), and 2 h into recovery after the WBV exposure (6 h) in all four exposure conditions. The results showed that a single, 4-h acute exposure to WBV may not be sufficient to induce skeletal muscle damage, inflammation or physiologic stress measurable in the blood. No significant differences were observed between conditions for any of the biomarkers that could be attributed to the exposure contrast between vertical-dominant and multi-axial WBV exposures. These findings further indicate known complications of WBV exposure likely arise secondary to chronic, repeated exposures that give rise to subclinical stresses that were not captured here.

Whole-Body Vibration Associated with Dozer Operation at an Australian Surface Coal Mine

Bulldozers are used extensively on surface mine sites and have been previously identified as being associated with high amplitude whole-body vibration exposures. Previous investigations of this equipment have involved either a very small number of measurements, or measurements of very short duration (or both); or the data obtained were incompletely reported. This research reports 69 measurements (median duration 440 min) obtained from 15 different dozers during operation at a surface coal mine. More than one-third of vertical vibration measurements exceeded the ISO2631.1 Health Guidance Caution Zone when expressed as VDV(8). Considerable variability in measurement amplitudes was found. This was also true within measurements obtained from the same dozers on different shifts suggesting, by a process of elimination, that the remaining variability in whole-body vibration amplitude is a function of some combination of task characteristics, geology, and operator behaviour; rather than equipment-related variability, such as maintenance, suspension, seating, or track design. Short-comings in the evaluation methods provided by ISO2631.1 are highlighted.

A Review of Low-Frequency Active Vibration Control of Seat suspension Systems

As a major device for reducing vibration and protecting passengers, the low-frequency vibration control performance of commercial vehicle seating systems has become an attractive research topic in recent years. This article reviews the recent developments in active seat suspensions for vehicles. The features of active seat suspension actuators and the related control algorithms are described and discussed in detail. In addition, the vibration control and reduction performance of active seat suspension systems are also reviewed. The article also discusses the prospects of the application of machine learning, including artificial neural network (ANN) control algorithms, in the development of active seat suspension systems for vibration control.

Prioritization of practical solutions for the vibrational health risk reduction of mining trucks using fuzzy decision making

The goal of this article was to prioritize the practical solutions for vibrational health risk reduction of truck drivers during mining operation using the multicriteria decision-making (MCDM) techniques. Mining trucks require special consideration because of their specific suspension system, large size, payload capacity, and off-road conditions of mining. In most cases, it is not easy for decision makers to compute verbal and linguistic variables, whose values are expressed in linguistic terms. These uncertainties and ambiguities are well interpreted by using fuzzy set theory. In this study, the MCDM methods were used under fuzzy environment. As a result, seat suspension maintenance was offered as the best solution to attenuate the vibrations and decrease the injuries related to the WBV exposure. The driver training, haul road construction and maintenance, lighting and visibility improvement and work organization were found as the other solutions, respectively.

Three-dimensional global acceleration estimation in the presence of rotation using an inertial measurement unit for whole-body vibration studies

Off-road vehicle operators are likely exposed to not only a high level but also different types of whole-body vibration (WBV) such as significant non-vertical and/or rotational accelerations. To evaluate the effects of these different WBV exposures, it is necessary to first correctly estimate the acceleration of the vehicle considering not only translational but also rotational motion. The main objective of this study was to propose and evaluate an algorithm to accurately estimate global acceleration of a vehicle using magnitude-based filtering and inertial navigation with an inertial measurement unit. In a laboratory experiment where a 6-df robotic arm generated three-dimensional motion at three different frequencies (2.3, 4.5 and 8.5 Hz), local acceleration data were collected in the presence of rotational movements. The comparison of the calculated global acceleration to the reference data show that the algorithm provides a good estimation of global acceleration even when rotational movement is not negligible.