Evaluation of the biodynamic response of the hand-arm system and hand-tool designs: a brief review.

Hand-operated tools transmit a high magnitude of vibration exposure to the hand-arm system that causes occupational diseases. The health effects caused in various countries for the past years due to usage of hand tools are necessary to identify the occupational disorders. Researchers have conducted various studies on biological effects, hand-transmitted vibration exposure and biodynamic responses throughout the years. This article goes over each of these studies in detail, as well as identifying areas where more research is needed. The majority of studies deal with the following topics: general guidelines for hand-transmitted vibrations; assessment techniques of vibration exposure; hand-tool evaluation methods; influence of hand-tool design to overcome the biomechanical effects; and finite element modelling for quantifying vibration exposure. In response to this, understanding the biodynamic behaviour of the hand-arm system is useful for better ergonomic intervention in hand tools to reduce fatigue and increase comfort.

Simulation of L-4 lumbar spine model of motorist exposed to vibration from speed hump.

BACKGROUND: The motorcycle is often used in recurring travel between locations, dense traffic, poor conditioned roads and thus the repetitive loading on the musculoskeletal system of the rider leads to risk factors associated with musculoskeletal disorders. This study was aimed to examine the biomechanical response of the L-4 lumbar spine while riding the motorcycle on the speed hump at 20 km/h. METHODS: Three-dimensional (3D) model of the L-4 lumbar spine was reconstructed based on the CT scan data obtained from the subjects. Material properties of the L-4 lumbar spine were assumed to be isotropic and homogenous. Mesh convergence and sensitivity analyses were performed and validated before simulation. Static and dynamic analyses were accomplished using quasi-static and steady-state dynamic analyses. RESULTS: Static analysis results show that the highest stress concentrations were found around the pedicle and spinal canal. It is an expected commonplace for injuries because of loading. The dynamic simulation results showed the major resonance of the L-4 lumbar spine model is about 8-40 Hz. The stress, displacement, velocity, and acceleration value declines beyond 40 Hz as the frequency increases. CONCLUSIONS: The simulation specifies the symmetric and unsymmetrical distributions of vibration magnitude regions of the lumbar spine. This study provides the modelling of the lumbar spine (L-4) and validated the effect of overloading failure as well as identified the biomechanical behaviour.

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

BACKGROUND: 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. OBJECTIVE: This study aimed to examine the influence of handle shapes in reducing the transmission of hand-arm vibration. METHODS: 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. RESULTS: 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%). CONCLUSIONS: 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.

Computer-aided human factors analysis of the industrial vehicle driver cabin to improve occupational health.

Industrial vehicle operator's solace and safety have gained significant consideration because of the increment in occupational health issues and accidents. The purpose of this work was to amend the design of the excavator driver cabin through human factor analysis. Thirty operators of excavators who were serving as subjects, were interviewed and identified that their wrist, upper arm and trunk were at a higher risk level while operating. Photograph of the operators was taken and the work environment was simulated. RULA (Rapid Upper Limb Assessment) and REBA (Rapid Entire Body Assessment) scoring was made on different simulated work posture of operators using CATIA V5 and UEAT1.8 softwares. Based on overall RULA and REBA scoring, it was found nearly 46% of the operators were operating at a high hazard level and needed investigation immediately, whereas 35% of operators were at a medium risk level and only 19% of operators were operating safely. The individual RULA and REBA scoring proved prevalence of discomfort in wrist, upper arm and trunk while operating. Identifying the optimized conditions to hold the control levers will help to reduce the operator strain. From the design optimization in excavators, the optimal conditions to hold the control lever is found to be 40cm for popliteal height, 60.51 cm for distance from elbow to ground and 15.07º for reach angle from the seat reference point.