Frequency-weighted Root Mean Square Research Articles

A Critical Assessment of Boundary Limits of Health Risks Associated with WBV Exposure Based on Field Studies on LHD Vehicles in Indian Underground Coal Mines

Purpose: The mining sector plays a pivotal role in meeting global resource demands, necessitating the extensive use of heavy earth-moving machinery (HEMM). Among these, load-haul-dump (LHD) mining vehicles are vital but expose operators to whole-body vibration (WBV) and shocks during their duties. Research indicates potential health risks associated with occupational WBV exposure, including musculoskeletal disorders. Evaluating these risks typically employs ISO 2631-1:1997, which, however, has limitations in addressing long-term exposure and shock effects. Methods: This study quantifies the health risks of LHD operators in Indian underground coal mines using ISO 2631-5:2018 and compares it to ISO 2631-1:1997. The methods for risk quantification from WBV vary between the two standards, leading to a comprehensive comparison. In addition, a cross-sectional study was undertaken to assess self-reported musculoskeletal pain among LHD operators. Results: The results were compared in accordance with frequency-weighted root mean square (RMS) values, vibration dose values (VDV), daily compressive dose (Sd A), and the risk of injury (RA) factor. The assessment using A(8), VDV, Sd A, and RA produced diverse evaluations, influencing varying perspectives on occupational health despite significant risks. ISO 2631-5:2018 consistently suggested a lower health risk for LHD operators as opposed to ISO 2631-1:1997. Seat effective amplitude transmissibility (SEAT) values showed amplification of vibration in the range of 4-8 Hz. Self-reported musculoskeletal pain indicated the prevalence of discomfort among operators. Conclusion: The study emphasizes a cautious approach when interpreting results and shaping guidelines to ensure sustainable development through the well-being of mining industry workers.

Vibration Control and Ride Comfort Analysis of a Full Car with a Driver Model Using Big-Bang Big-Crunch Optimized FLC

The main motive of the active suspension system is to enhance the ride comfort by suppressing the vibrations induced due to road irregularities. The actuator is getting more significance in the automotive industry due to its superior ride comfort for passengers. In this study, an eight Degrees of Freedom (DOF) full car with a driver model is considered for the ride comfort analysis (ISO2631 Standard) and vibration control. The real road terrain is not uniform in nature. Hence an effective intelligent control technology is required to improve the quality of travel. Initially, a conventional Proportional Integral and Derivative (PID) controller is designed for the system. Then a Fuzzy Logic Controller (FLC) is designed for the 8 DOF vehicle model to control the unwanted vibration produced in the vertical and angular directions. The FLC is designed with suitable firing rules, membership functions, and scaling factors using MATLAB/Simulink 2019 environment. The performance of FLC is further enhanced by the Big Bang Big Crunch (B3C) optimization technique, and it can suppress vibrations when the vehicle is travelling over bumpy and imperfect random road terrain as per ISO 8608. The Root Mean Square (RMS), Frequency Weighted RMS (FWRMS), and Vibration Dose Value of seat acceleration are the performance indices to investigate the potency of B3C-tuned FLC against the PID controller, FLC and passive suspension system.

Prescribed Performance Control-Based Semi-Active Vibration Controller for Seat Suspension Equipped with an Electromagnetic Damper

Seat suspension plays a vital role in improving riding comfort and protecting drivers’ health. This paper develops semi-active seat suspension that equips a controllable electromagnetic damper (EMD) and proposes a prescribed performance control-based semi-active vibration controller with experimental validation. The semi-active EMD mainly consists of a permanent magnet synchronous motor, a ball screw, a three-phase rectifier, and a controllable external resistor, which can vary its damping from 90 to 800 N·s/m by tuning the controllable external resistor in real-time. The EMD is applied to seat suspension, and a semi-active controller is proposed for the EMD seat suspension. In order to control the seat suspension vibration, a prescribed performance method is applied to obtain a desired control force and then a force-tracking strategy is designed to make the EMD track the desired control force. Finally, the semi-active seat suspension with the proposed controller is tested in experiments with different vibration conditions. The semi-active seat suspension performs excellently for the bump, sine wave and random vibration. The root mean square (RMS) acceleration, the frequency-weighted RMS acceleration and the acceleration’s fourth power vibration dose value were reduced by 17.5%, 39.9%, and 25.4%, respectively, in the random vibration, compared with a passive system.

Time integration algorithm of velocity frequency-weighted root mean square for ship comfort index

Time integration algorithm of velocity frequency-weighted root mean square for ship comfort index

Time integration algorithm of velocity frequency-weighted root mean square for ship comfort index

Time integration algorithm of velocity frequency-weighted root mean square for ship comfort index

Investigations of hand transmitted vibrations and associated health risks in load haul dumper operators based on different components of a work cycle

Load Haul Dumpers (LHDs) are operated in underground mines to transport ore/waste rock under extreme conditions. The operating conditions of the LHDs make the operators susceptible to occupational vibration exposure, including Hand Transmitted Vibrations (HTVs). To date, no research literature is available concerning the evaluation of HTVs based on different components of the LHD work cycle. In the present research study, HTV data were collected by mounting a hand strap on tri-axial accelerometer to the operator's hand in contact with the steering device of the LHDs. Frequency-weighted root mean square (WRMs) acceleration values for all the three measurement axes were collected during different components of the LHD work cycle, namely mucking, loaded travel, unloading, and empty travel. High vibration responses were recorded during the mucking operations, followed by empty hauling. Out of the eight LHDs considered for the study, three LHDs had total daily vibration values A(8) more than that of the stipulated Exposure Action Values (EAV) of 2.5 m/s2, the highest recorded being 2.9 m/s2 in the LHD designated L-6. Health risk assessment was carried out based on EU Directive 2002 and ISO 5349:2001, which showed that operators of three LHDs were at risk of developing health issues such as finger blanching within 12 years of their work life. Strategies to mitigate HTVs should focus on the component of the work cycle and the dominant axis of vibration along with the total daily vibration magnitudes. Operating the LHDs using remote controls during mucking can significantly reduce the total vibration magnitude within daily exposure limits.

Role of whole-body vibration exposure and posture of dumper operators in musculoskeletal disorders: a case study in metalliferous mines

Objectives. The combined role of whole-body vibration (WBV) exposure and awkward posture on musculoskeletal disorders (MSDs) experienced by dumper operators in two metalliferous mines in India was evaluated through a cross-sectional study. Methods. Frequency-weighted root mean square (rms) acceleration was used for WBV exposure assessment. Anthropometry and rapid upper limb assessment (RULA) were used for static and dynamic posture assessment, respectively. Prevalence of MSDs was assessed using the Nordic musculoskeletal questionnaire (NMQ). Logistic regression was used to assess the factors contributing to MSD problems. Results. The rms values revealed that the operators exceeded the lower limit of Standard No. ISO 2631-1:1997. The dynamic posture study revealed that the majority of dumper operators were taking awkward postures and 58–74% of them were subjected to high and medium levels of MSD risk. The adjusted odds ratio (7.96, 95% confidence interval [1.24, 41.35]) for the most awkward postures revealed WBV exposure as the significant risk factor for MSD problems among the operators. Conclusion. WBV exposure and posture of operators should be regularly monitored and corrective actions implemented to reduce their MSD problems. Ergonomic seat design based on the anthropometry of the operators should be assessed at the time of procuring new equipment.

Whale-optimized fuzzy-fractional order controller-based automobile suspension model

The functionality of the Active Suspension System (ASS) concerning stability and ride quality offers scope in modelling and simulation of automobile active suspension model. This work explores the design and simulation of a five degree of freedom ASS based driver integrated half car model (i.e.) Active Half Car Driver (AHCD) model. A novel design approach which assesses the Fuzzy-Fractional Order PID (FFOPID) controller parameters using bio inspired Whale Optimization Algorithm (WOA) is presented. The WOA is employed to manipulate the parameters of FFOPID controller and its efficacy is investigated using a comparative study against the performance of FOPID, FFOPID and Particle Swarm Optimization (PSO) technique tuned FFOPID (PSO-FFOPID) controllers over a single bump and a random road. The ACHD model is also analyzed under different speed levels which discloses performance adaptability of the proposed WOA-FFOPID controller. The Frequency Weighted Root Mean Square and Vibration dose value as per ISO 2631-1 standards are calculated and the results thus acquired are compared comprehensively and are analyzed which confirms that the WOA-FFOPID centered AHCD model provides the best ride comfort by reducing the driver body vibration in vertical motion.

Occupational exposure of dumper operators to whole-body vibration in opencast coal mines: an approach for risk assessment using a Bayesian network

Whole-body vibration (WBV) is one of the leading risk factors for development of musculoskeletal disorders (MSDs) that develop symptoms of lower back pain, pain in the neck and shoulders, digestive problems, blood pressure and diabetes among professional dumper operators. The present study specifically aimed at assessing the WBV exposure of 79 dumper operators engaged in two Indian opencast coal mines through vibration measurements followed by questionnaire survey. From the daily frequency-weighted root mean square exposure, dumper operators have experienced vibration levels higher than the Health Guidance Caution Zone (HGCZ) of Standard No. ISO 2631-1:1997. However, on the basis of daily vibration dose values, 60.8% of operators have experienced vibration levels above the HGCZ. Finally, an attempt was also made to explore the potential of a Bayesian network to predict the risk factors for WBV of dumper operators in development of MSDs to prioritize the factors for human health risk assessment.

Adaptive-Fuzzy Fractional Order PID Controller-Based Active Suspension for Vibration Control

ABSTRACT Active suspension system has become an integral part of a passenger vehicle as ride comfort is now an essential parameter in the performance of a vehicle. The active suspension system claims complete control over the driver body motion, thus improving the overall ride quality. This work intends to reduce the entire body acceleration of the driver, thereby improving the ride comfort by designing and implementing an efficient controller for an active quarter car system. The proposed Adaptive Fuzzy tuned Fractional Order PID Controller (AFFOPID) is designed and analyzed for a 3 Degree of Freedom (DOF) active quarter car system, incorporating a driver model using MATLAB/SIMULINK software. The efficiency of AFFOPID is dissected against the performance of Fractional Order PID (FOPID), PID and Passive System. The Active Quarter Car Driver model (AQCD) is exposed to single bump, sinusoidal bump and ISO 8606 standards random road for interruptions and the respective results are reviewed. The simulation outcomes of the active quarter car driver model with AFFOPID improve the ride comfort by reducing the Driver Body Acceleration (DBA) amplitude, over all three road profiles. The results, thus validated in-terms of Frequency Weighted Root Mean Square (FWRMS) and Vibration Dose Value (VDV) as per ISO 2631–1 standards, reveal that the AFFOPID reduces the vibration to the best desirable range in comparison to the contemporary FOPID and PID controllers.

Musculoskeletal Disorders Among Dozer Operators Exposed to Whole-Body Vibration in Indian Surface Coal Mines

Dozer operators are frequently exposed to whole-body vibration (WBV) during the execution of their work. Occupational exposure to WBV in Indian surface coal mines was evaluated by measuring vibration intensity and duration of exposure. A triaxial accelerometer was placed on the operator seat surface for taking the readings. Based on frequency-weighted root mean square acceleration equivalent to 8-hr shift duration, i.e., (A(8)) all dozer operators have exceeded an Exposure Action Value (EAV) of 0.5 m/s2, and 90% of dozers did not exceed Exposure Limit Value (ELV) of 1.15 m/s2. Based on Vibration Dose Value (VDV (8)), all dozer operators have exceeded Exposure Limit Value (EAV) of 9.1 m/s1.75, but no dozer operators have exceeded Exposure Limit Value (ELV) of 21 m/s1.75. Further, an epidemiological study was performed for identifying the extent of musculoskeletal disorders (MSDs) among dozer operators. For the detailed study, 42 dozer operators and 22 controls were selected from 2 surface coal mines. The control group was not exposed to WBV. It was seen from the cross-sectional study that pain in the lower back was predominantly higher (83.33%) in the exposed group when compared with the control group (31.81%). Likewise, pain in the neck (47.61%), shoulder (42.85%), knees (42.85%), and ankle (11.90%) was higher in the exposed group than that of the control group (22.71%, 0%, 45.45%, and 4.54%). A significant observation among the exposed group was that there was degradation in the quality of life. The outcome of the study would assist in monitoring and mitigation of machinery-induced vibration diseases (MIVD) in India and generally applicable to most of the mechanized mines as well. However, comprehensive studies are still needed to enunciate the magnitude extent.

One-third Octave Bandpass Filter Algorithm of Overall Frequency-weighted Root Mean Square for Comfort Index Applied to Acceleration Sensor

One-third Octave Bandpass Filter Algorithm of Overall Frequency-weighted Root Mean Square for Comfort Index Applied to Acceleration Sensor

Evaluation of Whole Body Vibration (WBV) of Dumper Operators Based on Job Cycle

Dumper operators are frequently exposed to whole body vibration (WBV) in surface mines. Surface mining activities involve the amalgamation of comparatively high intensity of vibration and extended exposure durations. Efficient risk reduction mandates knowing of important phases of a task that poses a threat to health of dumper operators. So far in India very limited studies have been reported on WBV exposure with regard to surface mines. This paper evaluates WBV of dumper operators based on ISO 2631-1:1997 Standards and European Union (EU) Directive 2002 for different phases of job cycle. Six dumpers were considered for this study and the vibration measurements were made for all the four phases of the job cycle by placing the triaxial accelerometer on the operator’s seat-surface and at the seat-back, independently. The findings of the study revealed that the haulage task (loaded travel and empty travel) remains the chief contributor to vibration exposure according to seat-surface and seat-back measurements. Maximum frequency weighted root mean square (RMS) of 1.12 m/s2 and 1.09 m/s2 were reported for empty travel task for seat-surface and seat-back measurements, respectively. For seat-surface measurements based on RMS, Z axis remains as the dominant axis of vibration for all the dumpers during haulage task, whereas for seat-back measurements, the dominant axis varies between X and Y. Exposure action value (EAV) based on RMS has exceeded the threshold value of 0.5 m/s2 for all the dumpers during loaded travel and empty travel for seat-surface as well as for seat-back measurements.

An electromagnetic variable inertance device for seat suspension vibration control

Abstract This paper designs and builds an electromagnetic variable inertance (VI) device for a heavy duty vehicle seat suspension to reduce the vibration transferred to driver bodies. The conventional semi-active vibration control mainly applies the variable damping (VD) and variable stiffness (VS) devices. The VI device is equivalent to an inerter with the capability to vary its inertance, which is a new semi-active system inspired by the VS device design. The VI device consists of a transmission device, a VD device and two flywheels. By varying the damping of the VD device, the equivalent inertance of the VI device is controllable in real time. The VI device prototype is built with an electromagnetic VD device which is controlled by the duty cycle of the pulse width modulation signal. The test results verify the proposed system model and identify the unknown model parameters. Then, a seat suspension applies the VI device prototype for improving the ride comfort. Based on the system model, an implementable controller is proposed and experimentally validated. The proposed seat suspension system shows excellent performance in a random vibration experiment. Compared with a conventional passive seat suspension, the frequency-weighted root mean square acceleration of the proposed one reduces 35.7%. The VI device has expanded the application of the inerter and the area of the semi-active research; it shows great potential in vibration control.

Evaluation of Whole-Body Vibration (WBV) of Dozer Operators Based on Job Cycle

Dozer operators are frequently exposed to high levels of occupational vibration. So far, no study reported component wise evaluation of dozer cycle of operation. In the present study, WBV data were collected by placing the trial accelerometer at operator’s seat-surface and at seat-back. Frequency-weighted root mean square (RMS), vibration dose value (VDV) and crest factor were collected for each dozer for two phases’ forward motion and return motion. All the dozers under study were found to be in severe zone with respect to measured RMS, during forward motion and return motion, irrespective of type of measurements (i.e., seat-surface and seat-back). As per VDV, out of eight dozers three dozers were found to be in caution zone during forward motion and three in return motion. According to EU Directive 2002 (as per RMS), all the dozers under study have reported exposure action value above 0.5 m/s2. Further, out of eight dozers, four dozers have shown exposure limit value above 1.15 m/s2 for seat-surface measurements and three dozers for seat-back measurements. Vibration mitigation strategies should be adapted not just based on intensity of vibration but also with respect to dominant axis of vibration. Considering the severe health risk due to the translational vibration (i.e., in x-direction), the vibration risk in the forward x-direction can be reduced by using seat belt; similarly in rear x-direction it can be attenuated by placing lumber-assisted back rest.

Influence of handle shape and size to reduce the hand-arm vibration discomfort.

Non-automated tool handles transmit a large magnitude of vibration to operators' hands, causing discomfort and pain. Therefore, the need for a better handle design is a matter of prime concern to overcome musculoskeletal disorders such as hand-arm vibration syndrome. This study aimed to examine the influence of handle shapes in reducing the transmission of hand-arm vibration. Seven different handles were designed and fabricated using 3D printing technology at the SSN College of Engineering, with consideration for the anatomical shape of the hand. The frequency-weighted Root Mean Square (RMS) values of the vibration levels transmitted were recorded at the wrist of twelve subjects, unaffected by musculoskeletal disorders. Subjective ratings of vibration and comfort perception were measured using the Borg Scale of Perceived Exertion. The total vibration value (ahv) of each of the six novel prototype handles (B-G) was compared to that of the reference handle denoted handle-A. The vibration reductions for handles B to G respectively were 0.542 m/s2 (14.59%), 0.481 m/s2 (12.95%), 0.351 m/s2 (9.45%), 0.270 m/s2 (7.27%), 0.407 m/s2 (10.96%) and 0.192 m/s2 (5.17%). A significant level of vibration reduction was achieved by the prototype handles. Qualitative feedback from the study subjects suggests that they were not aware of the levels of vibration being transmitted to the hand with each handle.

Artificial neural network predication and validation of optimum suspension parameters of a passive suspension system

This paper presents the modeling and optimization of quarter car suspension system using Macpherson strut. A mathematical model of quarter car is developed, simulated and optimized in Matlab/Simulink® environment. The results are validated using test rig. The suspension system parameters are optimized using a genetic algorithm for objective functions viz. vibration dose value (VDV), frequency weighted root mean square acceleration (hereafter called as RMS acceleration), maximum transient vibration value, root mean square suspension space and root mean square tyre deflection. ISO 2631-1 standard is adopted to assess ride and health criterion. Results shows that optimum parameters provide ride comfort and health criterions over classical design. The optimization results are experimentally validated using quarter car test setup. The genetic algorithm optimization results are further extended to the artificial neural network simulation and prediction model. Artificial neural network model is carried out in Matlab/Simulink® environment and Neuro Dimensions. Simulation, experimental and predicted results are in close correlation. The optimized system reduces the values of VDV by 45%. Also, RMS acceleration is reduced by 47%. Thus, the optimized system improved ride comfort by reducing RMS acceleration and improved health criterion by reducing the VDV. Finally ANN can be used for predicting the optimum suspension parameters values with good agreement.

A rotary variable admittance device and its application in vehicle seat suspension vibration control

In this paper, a novel semi-active variable admittance (VA) concept is proposed, and a seat suspension prototype with a magnetorheological fluid damper based rotary VA device is designed, manufactured, and experimentally validated. The conventional inerter with a single flywheel has a constant inertance, which can effectively improve the suspension performance by being integrated into a mechanical network with springs and dampers. The proposed rotary VA device comprises a gear reducer, two flywheels and a variable damping (VD) device which is used to connect the two flywheels. With carefully designing, the rotary VA device is compacted and is similar with a VD device in size. The rotary VA device is installed in the centre of a seat suspension's scissors structure to form a VA seat suspension. According to the test results, the equivalent inertance of the seat suspension can vary from 11.3 Kg–76.6 Kg with a 3 Hz frequency and 5 mm amplitude sinusoidal movement by changing the current from 0 A–1 A. By analysing the system characteristics, a hybrid controller with two acceleration feedbacks is proposed. Thereafter, the seat suspension and controller are validated in experiments by comparing the performance with a conventional passive seat suspension. The random vibration test shows the excellent performance of the proposed seat suspension; the frequency weighted root mean square acceleration of the seat is reduced by 43.6%, which indicates a great improvement of the ride comfort. The VA device shows great prospect in the suspension application.

Monitoring and Evaluation of Whole-Body Vibration Exposure of Equipment Operators and Assessment of Associated Health Risk in an Indian Underground Pb-Zn Mine

Exposure to whole-body vibration (1-80 Hz) manifest in higher incidences of low back pain and other musculoskeletal disorders among the workforce in mining industry. The aim of the study was to determine the vibration intensity of twelve mining equipments which are regularly deployed in an underground mine and to evaluate the long term health risk of their operators as per ISO 2631-1:1997 guidelines. It was observed that the low profile dump trucks (LPDT) and load haul dumpers (LHD) had x axis (front-back) as dominant axis of vibration. The operators of LPDTs and LHDs had moderate health risk considering frequency weighted root mean square (r.m.s.) acceleration values of vibration (0.46 – 1.01 m/s2) and corresponding daily exposure of about 6 hours in a shift. Operators of three equipments i.e. water sprinkler, utility vehicle and backfill material carrier had high health risk with z (vertical) as dominant axis of vibration. RMS acceleration values were comparatively high (1.30- 1.96 m/s2) even though their duration of exposure was less (2.5-5.0 hours). Motor grader operator had minimal health risk from vibration exposure while rest two operators of explosive and personnel carrier had moderate health risk. Additional assessment of health risk was carried out using total vibration dose values wherever applicable. High health risks were attributed to fast and harsh driving, poor seat condition and absence of independent seat suspension. Besides technical and operational modifications, training programs should be organised to improve the awareness of this hazard among miners in India.

Control of a multiple-DOF vehicle seat suspension with roll and vertical vibration

In this paper, the control of roll vibration and vertical vibration of a seat suspension caused by uneven road under both sides of tyres is studied. The heavy duty vehicles are generally working under severe conditions, where the uneven road can cause roll vibration and vertical vibration of the vehicle body and can have an effect on seat suspension. The conventional single-degree of freedom (single-DOF) seat suspension can only isolate the vertical vibration while the roll vibration will be totally transferred to the driver's body. The high magnitude of driver body's lateral acceleration caused by roll vibration will influence drivers' health and have a negative effect on ride comfort. A two-layer multiple-DOF active seat suspension, which has a z-axis DOF in the bottom layer and a roll DOF in the top layer, is proposed in this paper. A non-singular terminal sliding controller is designed to control the top-layer to reduce the lateral acceleration and roll acceleration by tracking a desired roll angle. An H∞ controller with disturbance compensation is applied to control the bottom-layer for vertical vibration isolation. Both controllers use the variables which can be measured or estimated in the practical application as feedback signals. Two inertial measurement units (IMUs) MPU9250 are used in order to estimate the rotary angles of the top and base platforms of the two-layer multiple-DOF active seat suspension. The effectiveness of the seat suspension and control method is validated by both simulations and experiments. A single-DOF active seat suspension and a well-tuned conventional passive one are applied for comparison. Based on ISO 2631, the vibration total value of frequency weighted root mean square (FW-RMS) acceleration of the multiple-DOF active seat surface has 29.8% and 23.6% reductions for evaluating its influence on health and ride comfort, respectively, when compared with the single-DOF active one. The proposed vibration isolation method can effectively reduce the whole body vibration (WBV) of heavy duty vehicle drivers, and it shows high potential for practical application.