Characterization and control of human responses to global and local vibration

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Proposed study concerns control of global vibration (WBV) of vehicle drivers and localized hand-transmitted vibration (HTV) of power tools operators via engineering interventions. Operators of hand-held power tools in industrial sector are exposed to high magnitudes of HTV in broad frequency ranges (up to 2000 Hz). Occupational exposure to such vibration has been associated with vascular and neural disorders, collectively known as hand-arm vibration syndrome (HAVS). Similarly, work vehicle drivers are exposed to WBV predominant in low frequency range (up to 20 Hz). Exposure to WBV has been correlated with musculoskeletal disorders, particularly lower back pain and degenerative lesions of spine. Approximately 4 to7% of all employees in USA, Canada and European countries are potentially exposed to harmful vibration with annual costs of health care, compensation and lost workdays in the order of several billion dollars. Owing to health risks of vibration exposure, international standards and an EU directive have defined caution guidance and safe exposure limits. HTV and WBV exposures of operators, however, generally lie within the caution zone or exceed safe limits, suggesting need for effective engineering interventions, considering excessive health care and compensation costs apart from social well-being of the exposed population. Overall goal of this study is to build knowledge on human responses to WBV and HTV, and develop human-centered designs for limiting WBV and HTV exposures and potential injury risks, while ensuring HQP training with multi-disciplinary challenges. The specific goals include design of control methods for isolation of hand from vibrating tool handle, developments in low vibration impact tools, control of vertical WBV via vehicle-specific suspension seats, and control of multi-axis WBV exposure via an innovative inter-axle coupled hydro-pneumatic suspension. Owing to significant absorption of vibration energy by the seated body and hand-arm system (HAS), the design approaches involved developments in biodynamic models of HAS and seated body. These are integrated to models of a percussion tool and seat, respectively, to obtain coupled hand-tool and body-seat models for deriving optimal human-centered designs of vibration control devices. Study aims to develop optimal antivibration gloves for control of HTV considering contributions due to hand-handle coupling forces and HAS biodynamics. A tuned vibration absorber is proposed for control of vibration of an impact tool. A vehicle-specific seat suspension design methodology is proposed for optimal control of vertical WBV exposure considering vibration absorption by seated body and uncertainties due to body mass and ride height variations, and occasional shocks. The control of multi-axis WBV exposure will be achieved by design of inter-axle coupled hydro-pneumatic suspension, which permits decoupling of modes and thereby preserve roll and directional stability of vehicle.