Evaluation And Experimental Study On Human Fatigue During Brush Cutting Operation Based On Ergonomics

Brush cutter operation is one of the most popular working method in modern forestry and agricultural laboring.Gardeners frequently use brush cutter to complete green operation when they trim weeds and shrubs.Meanwhile,famers frequently use brush cutter to trim weeds and harvest crops such as pasture,wheat,rice,barley and mulberry.When operating portable brush cutter,workers usually bear weight in a certain position.When workers expose to the natural environment,their workload will increase due to the bearing weight,working posture,vibration form the machine and noise,which can lead to working fatigue,occupational diseases and even working accidents.As a result,based on the theory of ergonomics,applying precise and reliable scientific evaluation methods as well as experimental measurement tools,it is especially necessary to study and evaluate human fatigue of workers operating the brush cutters.This study will ensure the decrease of the incidence of forest labour injury,which has become an essential issue in the field of human factors home and worldwide.In this context,based on biomechanics and mathematical analysis,this paper systematically studies and evaluates the human fatigue in brush cutting operation,specific research as follows:Based on the theory of ergonomics and statistics,this paper analyses the ergonomic factors which affects human fatigue in brush cutting operation,builds the multi-index evaluation system of human fatigue level in brush cutting operation,establishes evaluation procedures of human fatigue level in brush cutting operation,applies research methods such as questionnaire,observation and RULA to evaluate and assign every evaluation index,applies entropy evaluation method and analytic hierarchy process(AHP)to establish evaluation quantitative model of working fatigue level and then conduct calculation,verifies the accuracy of the evaluation quantitative model with the help of blood oxygenation experiment.Based on the theory of biomechanics and kinematics,this paper gathers workers’ dynamics and kinematics data when they use brush cutter to trim grasses,shrubs and branches with motion capture technology,and then the data are analysed by biomechanics software.Applying biomechanical method,this paper also establishes simplified mechanics models of different working posture when workers operate brush cutters in three different working conditions,analyses the activities and functions of the workers’trunk muscles in different working posture with surface electromyography(EMG),describes and evaluates load factors of human musculoskeletal fatigue in brush cutting operation.Root mean square value and total value of hand vibration accelerated speed are measures and analysed by three-dimensional coordinate system.These value of hand vibration comes from different cutting tools of two common brush cutters in engine idle,low-speed and high-speed operation.Then A(8)threshold of different knapsack brush cutter and the shoulder-hanging brush cutter’s cutting tools are gathered and the threshold are compared by current occupational health standards in China.White finger prevalence rate is evaluated with questionnaire statistics and cold water rewarming method.The relevance of vibration hazard symptoms and total vibration received by workers are evaluated by regression analysis.According to noise measurement of objective physical parameters in ergonomics and engineering psychology,the noise exposure metering and noise spectrum of every working day during workers operating the trimmer line are measured and recorded and the data are compared by current occupational health standards in China.Taking the impact of human psychological and physiological load caused by workers’ electroencephalogram as evaluative criteria,this paper analyses how brush cutter operation affects to workers’electroencephalogram and the relevance between the noise and workers’ working fatigue.Based on the research above,this paper points out the ergonomic design principles of brush cutter’s back pad and handle,establishes the human upper limb model and arm movement model in the brush cutting operation,calculates the length of the brush cutter’ s handle,puts forward brush cutters’ design principles on vibration absorption and noise reduction,tries to show a redesign programme of knapsack brush cutter which meets the ergonomic standard,uses JACK software to carry out ergonomics simulation evaluation,uses RULA and OWAS model to carry out human factor analysis of working posture in different working conditions separately.This research can provide theoretical reference to ascertain workers’ working fatigue when they operate brush cutters,which has important theoretical value and practical significance to study working posture,effects of vibration and noise on physical ability and physiological load,to design and improve brush cutter,to correct false working posture,to reduce working fatigue,to prevent and reduce occupational skeletal muscle damage,vibration hazard symptoms,to improve working efficiency,to improve workers’ occupational health and operational safety management.