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IE 553 Engineering of Human Work Dr. Andris Freivalds Class #28

IE 553 Engineering of Human Work Dr. Andris Freivalds Class #28. IE 553 Engineering of Human Work Dr. Andris Freivalds Class #28. Cycling Work. Lifting 8.25 lbs, 20 in., 6/min E ave = 1.5 kcal/min, E r = 1.3 kcal/min E w = [E ave (T w +T r ) - E r ×T r ]/T w.

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IE 553 Engineering of Human Work Dr. Andris Freivalds Class #28

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  1. IE 553 Engineering of Human Work Dr. Andris Freivalds Class #28 IE 553

  2. IE 553 Engineering of Human Work Dr. Andris Freivalds Class #28 IE 553

  3. Cycling 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]/Tw IE 553

  4. Metabolic 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 553

  5. Garg Model • Main assumptions (similar to MTM) • Ėjob = function of physical characteristics of job • Job broken down into simpler tasks • Ėjob = ∑ Ėtasks • Two components: • Maintenance of body posture = sitting (Eq. 6.1), standing (Eq. 6.2), standing bent (Eq. 6.3) • Net increase due to tasks Ėjob = [ ∑Ėposture × time + ∑ΔEtasks] / time IE 553

  6. Tasks - 1 • Vertical lift: • Stoop lift (V<32", Eq. 6.4) • Squat lift (V<32", Eq. 6.5) • Arm lift (V>32", Eq. 6.7) • Vertical lower: • Stoop lower (V<32", Eq. 6.8) • Squat lower (V<32", Eq. 6.9) • Arm lower (V>32", Eq. 6.10) IE 553

  7. Tasks - 2 • 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) • Push/pull: • 32" bench height (Eq. 6.17) • 60" height (Eq. 6.18) IE 553

  8. Tasks - 3 • 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) • Horizontal arm work: • Stand (Eq. 6.24) • Sit (Eq. 6.25) IE 553

  9. Major Variables/Modifiers • Individual characteristics: • Gender • Weight • Working style: posture, speed • Task characteristics: • Frequency • Load • Vertical range • Grade of surface • Horizontal distance moved IE 553

  10. Comments - 1 • Two regions for lift/lower: • 0-32“ (lift body weight) • >32“ (lift arms only) • Freestyle lift = average stoop & squat lifts • Lift and lowers could have horizontal component (in addition to vertical) IE 553

  11. Comments - 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 553

  12. Ex. #1: Box Lifting • 160 lb male, lifting 20 lb boxes, 10/min, from 30" bench to 40" conveyor • Required tasks? IE 553

  13. Garg’s Model IE 553

  14. Ex. #1: Box Lifting 160 lb male, lifting 20 lb boxes, 10/min, from 30" bench to 40" conveyor • 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/lift 2) 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/lift IE 553

  15. Ex. #1: Box Lifting – con’t 3) 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/lower 4) 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/lower Standing posture Ė = 0.0109BW = 0.0109(160) = 1.744 kcal/min IE 553

  16. Ex. #1: Box Lifting – Total Ė • Ėjob = [ ∑Ėposture × time + ∑ΔEtasks] / time • ∑ΔEtasks=10×[0.0235 + 0.0507 + 0.0115 + 0.0125] • = 0.982 kcal • Ėjob  = 1.744(1) + 0.982 = 2.73 kcal/min IE 553

  17. Validation • 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 553

  18. Garg’s Model IE 553

  19. IE 553

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