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IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #37

IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #37. Ch. 9 – Hand Tools. As old as mankind Flint striking stones Addition of handle increased energy Surprising variety (12,000 shovels) Addition of power But also injuries 6% of Worker’s Comp 10% of injuries.

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IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #37

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  1. IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #37 IE 552

  2. Ch. 9 – Hand Tools • As old as mankind • Flint striking stones • Addition of handle increased energy • Surprising variety (12,000 shovels) • Addition of power • But also injuries • 6% of Worker’s Comp • 10% of injuries IE 552

  3. General Tool Principles • Perform effectively • Fit the operator: size and strength • Not cause fatigue or injury • Provide feedback • Be relatively cheap IE 552

  4. Types of Grip IE 552

  5. Relative Forces for Types of Grip IE 552

  6. Mechanics of Gripping IE 552

  7. Relative Finger Forces IE 552

  8. Forces in Precision Grip IE 552

  9. Friction and Safety • Safety Margin = excessive pinch force above minimum needed to avoid tool slip • Force Ratio = Grip force Application force • Coefficient of friction: μ = W 2FP • Difficult to measure • Wide range: 0.2 < μ < 1.4 IE 552

  10. Above injury threshold Below injury threshold A = weak B = strong (contraction) Model of Pinch Force Injuries IE 552

  11. Grip Force Control Modulation = Fpmax- Fpmin Index Fpmax = a/b IE 552

  12. CTS & Grip Modulation Index Force Ratio IE 552

  13. Optimum Working Posture IE 552

  14. Grip Strength vs Wrist Position IE 552

  15. Finger Forces & Triggers IE 552

  16. Handles • Length: 71 – 97 mm • Diameter: 32-40 mm (31-39) • Overlap fingers • Depends on finger size • NHS = circumference = 55% hand length • NFS = circumference = 100% finger length • Shape → double frustum IE 552

  17. Angulation of Handle IE 552

  18. Grip Strength vs. Grip Span IE 552

  19. Pinch Strength vs. Grip Span IE 552

  20. Other Tool Considerations • Gender • Handedness • Weight • Gloves • Vibration • Sharp edges • Pinch points IE 552

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