Slide 1Slide 2Cycling WorkMetabolic Energy Prediction/ModelingGarg ModelTasks - 1Tasks - 2Tasks - 3Major Variables/ModifiersComments - 1Comments - 2Ex. #1: Box LiftingGarg’s ModelSlide 14Ex. #1: Box Lifting – con’tEx. #1: Box Lifting – Total ĖValidationSlide 18Slide 19IE 5531IE 553 Engineering of Human WorkDr. Andris FreivaldsClass #28IE 5532IE 553 Engineering of Human WorkDr. Andris FreivaldsClass #28IE 5533Cycling Work•Lifting 8.25 lbs, 20 in., 6/min•Eave = 1.5 kcal/min, Er = 1.3 kcal/min•Ew = [Eave(Tw+Tr) - Er×Tr]/TwIE 5534Metabolic Energy Prediction/Modeling•Need: actual measurements on job:–Difficult, interferes with task–Costly, can’t measure new task•Basis:–Table values (Passmore & Durnin, 1955):•Crude, inaccurate•Many new jobs not found–Predictive models: Ǻberg (1968), Garg (1978)IE 5535Garg Model •Main assumptions (similar to MTM)–Ėjob = function of physical characteristics of job–Job broken down into simpler tasks– Ėjob = ∑ Ėtasks•Two components:1) Maintenance of body posture = sitting (Eq. 6.1), standing (Eq. 6.2), standing bent (Eq. 6.3) 2) Net increase due to tasksĖjob = [ ∑Ėposture × time + ∑ΔEtasks] / timeIE 5536Tasks - 11) Vertical lift:•Stoop lift (V<32", Eq. 6.4)•Squat lift (V<32", Eq. 6.5)•Arm lift (V>32", Eq. 6.7)2) Vertical lower:•Stoop lower (V<32", Eq. 6.8)•Squat lower (V<32", Eq. 6.9)•Arm lower (V>32", Eq. 6.10)IE 5537Tasks - 23) Walk/carry/hold:•Walk (Eq. 6.11)•Carry arms length (Eq. 6.12)•Carry at waist (Eq. 6.13)•Hold arms length (Eq. 6.14)•Hold at waist (Eq. 6.15)•Hold out in one hand (Eq. 6.16)4) Push/pull:•32" bench height (Eq. 6.17)•60" height (Eq. 6.18)IE 5538Tasks - 35) Lateral arm work:•Both hands 180° (Eq. 6.19)•One hand 180° (Eq. 6.20)•Stand 90° (Eq. 6.21)•Sit both hands 90° (Eq. 6.22)•Sit one hand 90° (Eq. 6.23)6) Horizontal arm work:•Stand (Eq. 6.24)•Sit (Eq. 6.25)IE 5539Major Variables/Modifiers•Individual characteristics:–Gender–Weight –Working style: posture, speed•Task characteristics:–Frequency–Load–Vertical range–Grade of surface–Horizontal distance movedIE 55310Comments - 1•Two regions for lift/lower: 1) 0-32“ (lift body weight)2) >32“ (lift arms only)•Freestyle lift = average stoop & squat lifts•Lift and lowers could have horizontal component (in addition to vertical)IE 55311Comments - 2•Estimate speed: –2 mph = 88 steps/min–3 mph = 108 steps/min•Climbing stairs: –ΔE(per step) = 0.1 + 0.0014 (BW+L) •ACU: lbs, in, mph, %IE 55312Ex. #1: Box Lifting •160 lb male, lifting 20 lb boxes, 10/min, from 30" bench to 40" conveyor•Required tasks?IE 55313Garg’s ModelIE 55314Ex. #1: Box Lifting 160 lb male, lifting 20 lb boxes, 10/min, from 30" bench to 40" conveyor1) Stoop lift 30"→ 32" ΔE = 10-4[0.375BW(32-h1) + (1.63L + 0.875 S×L)(h2-h1)]ΔE = 10-4[0.375(160)(32-30) + (1.63(20) + 0.875(20))(32-30)] = 0.0235 kcal/lift2) Arm lift 32"→ 40" ΔE = 10-4[0.06BW(h2-32) + (3.22L - 0.53 S×L)(h2-h1)]ΔE = 10-4[0.06(160)(40-32) + (3.22(20) - 0.53 (20))(40-32)] = 0.0507 kcal/liftIE 55315Ex. #1: Box Lifting – con’t3) Arm lower 40"→ 32" (no load)ΔE = 10-4[0.09BW(h2-32) + (1.03L + 0.37 S×L)(h2-h1)]ΔE = 10-4[0.09(160)(40-32)] = 0.0115 kcal/lower4) Stoop lower 32" → 30" (no load)ΔE = 10-4[0.31BW(32-h1) + 0.78L(h2-h1) + 13.25 S(32-h1)]ΔE = 10-4[0.31(160)(32-30) + 13.25(2)] = 0.0125 kcal/lowerStanding posture Ė = 0.0109BW = 0.0109(160) = 1.744 kcal/minIE 55316Ex. #1: Box Lifting – Total Ė Ėjob = [ ∑Ėposture × time + ∑ΔEtasks] / time∑ΔEtasks = 10×[0.0235 + 0.0507 + 0.0115 + 0.0125] = 0.982 kcalĖjob = 1.744(1) + 0.982 = 2.73 kcal/minIE 55317Validation •Stepwise multiple regression, with 3 males and 3 females, r2 = 0.98•Literature: 20 tasks, difference of 2.9 to 38%, average = 13.8%•Field work: 16 tasks, average difference = 5.6%•Garg found overprediction•Beginners typically underpredict•Best feature = relative comparison for redesign (careful with absolute values)IE 55318Garg’s ModelIE
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