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人机工程学 Ergo 101 Part 2.pdf

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人机 工程学 ERGO 101 PART
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Ergo 101 Part 2 Ergonomic Risk Factors MODULE II 2 Copyright Sandalwood 2006 3 Risk Factors Big 3 = Posture + force + frequency ? Posture: ? Can cause pinching and impingement of tissues ? Increase moment arm of load, thus increasing overall force ? Force: ? external forces (object weight) ? Internal forces produced my muscles & passive tissues ? Frequency/repetition: ? can lead to progressive decrease in tissue tolerance level Adapted from author Jim Potvin, PhD, University of Windsor Module II 4 Force ? Force is the amount of energy: ?generated by body muscles (Force Generated) ?applied to an external object (Force Applied) ? Force Generated Force Applied ? The risk from force depends on: ?What part of the body is exerting force ?What kind of movement is involved ?The presence of other risk factors ? Module II 5 Force (Generated) ? Muscular force generation is defined in terms of % Maximum Voluntary Contraction (MVC) where: % MVC = Voluntary Contraction to perform task MVC under conditions task performed Module II 6 Force (Generated) ? Amount of force generation is dependent on: ?degree & type of muscle contraction ?postural deviation ?number muscles activated Module II 7 Force (Applied) ? Force Generated Force Applied ? Degree of force application is dependent on: ?force generated ?surface properties (i.e. friction, inclination) ?direction of force application ?object properties (i.e. weight, coupling) ? Module II 8 Force (Applied) ? Types of force application: ?initial ?sustained Cart pushing involves both initial & sustained forces Module II Force 9 Applied Generated (Body Weight/Load) (Back/Upper Arm) Module II Typical Force Issues: Module II Typical Force Issues.. continued: Module II 12 Risk Factors Big 3 = Posture + force + frequency ? Posture: ? Can cause pinching and impingement of tissues ? Increase moment arm of load, thus increasing overall force ? Force: ? external forces (object weight) ? Internal forces produced my muscles & passive tissues ? Frequency/repetition: ? can lead to progressive decrease in tissue tolerance level Adapted from author Jim Potvin, PhD, University of Windsor Module II Muscles ? Muscles work by contraction. ? When a muscle contracts, blood flow is constricted. ? When blood flow is constricted, muscles are deprived of oxygen and cannot eliminate waste. ? Muscles must have time to recover, after contraction, in order to repeat a task. 13 Module II 14 Frequency ? Optimal working rhythms occur by alternating muscular contractions & rest periods ? High muscular efforts & contraction time do not provide adequate allowances for rest ? If adequate rest is not taken during task performance, subsequent rest pauses taken will be less effective Module II 15 Frequency ? “Repetitiveness refers to a repeated sequence of muscular exertions or sustained postures over a given time period. ? The risk from repetition depends on: ?The kind of muscular movements involved ?The presence of other risk factors, as well as whether it is a static or dynamic task. Module II 16 Frequency ? Effects of muscular fatigue are cumulative in nature, such that only brief restorations of task performance may occur with latent rest periods (Adapted from Rohmert, 1973) Degree of fatigue Cumulative time Module II 17 Static Work ? Involves the continuous contraction of muscles ? Reduces tissue blood flow, nutrients, & waste product removal ? Frequent, prolonged static contractions will deteriorate the functional mobility of activated musculature Module II 18 Static Work Effects on blood flow during conditions of rest, and static, and dynamic contractions (Adapted from Grandjean, 1988) Module II 19 Static Work ? Most tasks incorporate intermittent static muscular contractions with dynamic contractions Static versus dynamic motions Module II 20 Static versus Dynamic Motions Module II Evaluate Job Stresses ? Ergonomics Risk Factors ?Stressful Postures ?Force ?Frequency ?Mechanical Stress ?Vibration/Torque 21 Module II 22 Mechanical Stressors (Point Loading) ? Tissue point loading may occur from exposure to a sharp, pointed & rough contact surfaces ? Effects include tissue blood flow reductions, pain, & fatigue Sharp worksurface edge Blunt tool handle Module II 23 Vibration ? Oscillatory motion about a fixed point ? Prolonged exposure results in tissue blood flow reductions and micro tissue tearing ? Two common forms of vibration: ?Localized (hand-arm) ?Whole body Module II 24 Vibration ?Exposure to localized vibration will increase: ? Increased hand grip force ? increase the amount of vibration transferred to the hand-arm segment ?Sources of localized vibration may include: ? poorly designed or maintained powered hand tools (eg. palm sanders, rivet guns) ? Contact with rotating or vibrating equipment Module II 25 Vibration ?Overexposure to whole body vibration is associated with: ? back discomfort & injury ? digestive track disorders ? neurovascular disorders ?Sources of whole body vibration include: ? vehicles ? oscillating floors / structures (eg. stamping facilities) Module II 26 Combination Effects of Risk Factors ?Risk factors usually have their harmful effects on the worker in some combination Module II 27 Combination Effects of Risk Factors Examples Module II Demand Capacity Injury Risk is proportional to: Demand Capacity INJURY Risk of Injury Module II Strength Capability 17lbs 15lbs 25% Female Rating Hose Insertion Continuous Improvement 25lbs 50lbs Engineering Must Change P o p u l a t i o n Male Female Protect 90% of Population (75% female & 99% male ) ERGO RED: Risk Assessment Scale Green RED
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