Study On Work Comfort Assessment Method Based On Musculoskeletal Load

In order to find out the bad working posture,relieve the fatigue of the body,so that the workers can work efficiently,safely and healthily,this paper propose a work comfort assessment method based on the characteristic of joint load and muscle fatigue to overcome the problems of the previous methods relying on expert experience,which are strong subjectivity and poor assessment effect.This method is based on primary muscle sEMG variation situation in different joint motion angles of the time domain index(maximum active contraction of myoelectric percentage)and frequency domain index(mean power frequency).The joint load data is obtained by virtual human model simulation.Entropy and correlation analysis are used to determine the influence of different joint motion changes on human comfort.The theory of fuzzy comprehensive evaluation is combined to assess work comfort.The main study of the paper is as follows1)In order to determine the influence of joint motion change to human body comfort,DELMIA ergonomics simulation software is used to perform joint load(joint force and joint torque)experiments on five upper limbs(neck joint,shoulder joint,elbow joint,wrist joint and lumbar joint).The change increment of joint motion is set according to the degree freedom of the joint and the range of joint motion.By using the software of the pose editor change posture of human body model,the joint load is given by the biomechanical analysis function module.Since the variation of each joint motion with angle has some effect on the torque of the five joints of the upper limb,entropy method is used to determine the weight of each joint action assessment index.By excluding joint moments that have no significant data changes after joint action change,and the correlation coefficients of joint and joint motions are obtained by analyzing the joint moment values affected by joint action.The weight of the assessment index determined by entropy method is obtained,and the weight of each joint action was determined by the composite correlation coefficient.2)According to the physiological characteristics of the cause and effect relationship between the changes of the surface electromotor signal and the muscle fatigue and the comfort level according to the degree of muscle tension contraction,and an experiment was conducted to study the effects of different joint action positions and loads on the changes of the sEMG signals in a group of subjects.Five joints of human upper limbs are selected for the test of sEMG.It use that physiological recorder of MP150 to measure the change of the sEMG signal of primary muscle in a group of subjects under different static joint actions.The difference of sEMG signals in different subjects was eliminated by the maximum active contraction method.The maximal active contractive myoelectric percentage of each joint action under three kinds of different loading conditions is given.With the rapid Fourier transform of the original sEMG signal,the method of polynomial fitting is used to calculate the slope of the mean power frequency(MPF)at different angles,and the changes rule of MPF under different joint action angles are obtained.According to the size of the cross-sectional area of the human muscle,the absolute value of the MPF slope value of all subjects was normalized and weighted,and the index of motion comfort of joints under different angles is given.3)The fuzzy assessment theory is applied to evaluate the work comfort.For the five joints and joint movements that are mainly involved in the upper limbs,a set of assessment factors of comfort was established.According to membership functions and weight of joint and joint motions,work comfort assessment method based on musculoskeletal loads is established by using two-stage fuzzy comprehensive assessment to assess each joint and comfort.Compared with the widely used rapid upper limb assessment method(RULA)in engineering,it can be seen that the change trend in the scores are almost identical.In this method,the joint score interval is finer and more accurate.For some joints,the changes of abduction,lateral flexion and rotation of the joint are considered more comprehensively,which can reflect the condition of work comfort more comprehensively.In view of the influence of job load on work comfort,the joint comfort level can be changed accurately according to the change of maximum active contraction electromyogram percentage with angle.