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Hand Tools I

Hand Tools I. Rad Zdero, Ph.D. zradovan@uoguelph.ca University of Guelph. Outline. Hand Anatomy & Injury Design Principles Shape Orientation Size Weight Grip Strength Vibration Texturing and Gloves. Hand Anatomy & Injury. Bones of the Hand. [Hall, 1999]. Nerves & Arteries of

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Hand Tools I

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  1. Hand Tools I Rad Zdero, Ph.D. zradovan@uoguelph.ca University of Guelph

  2. Outline • Hand Anatomy & Injury • Design Principles • Shape • Orientation • Size • Weight • Grip Strength • Vibration • Texturing and Gloves

  3. Hand Anatomy & Injury

  4. Bones of the Hand [Hall, 1999]

  5. Nerves & Arteries of the Hand Transverse Carpal Ligament Ulnar Nerve Pisiform Bone Radial Artery Ulnar Artery Median Nerve Tendons [Tichauer, 1978]

  6. Movements of the Hand Neutral Neutral [Hall, 1999]

  7. Hand Injury and Disorder Traumatic “One Time” Injuries • impact, crush, cut • 9 % of all work-related injuries • 260,000 hand tool related injuries in U.S. each year • $ 400 million associated medical costs • 21% of hand injuries are power tool related • Most common: knives, wrenches, and hammers • Mostly “one time” traumatic injuries (U.S. Statistics by Aghazadeh & Mital, 1987)

  8. Hand Injury and Disorder • Repetitive Injuries • 4.8 % of workers in meat packing industry suffer from repetitive injuries (Bureau of Labor Stats, 1986) • 13 repetitive injuries per 200,000 work hours in poultry processing plant (Armstrong et al., 1982) • Often go unreported but show up as … • reduced worker output • poor quality work • increased absence from work • “one time” trauma injuries

  9. Hand Injury and Disorder Carpal Tunnel Syndrome • hand held in fixed position for prolonged time • repetitive exertion with flexed or hyperflexed wrist with low or high forces • pressure at base of palm • vibration Tendinitis • repetitive motion, especially in combination with ulnar deviation with fixed thumb Hammer Syndrome • vibration, push, twist, hand hammering, catching

  10. Hand Injury and Disorder • Trigger Finger • excessive flexion and extension of digits • overuse of finger with pistol airtool • Gamekeeper’s Thumb • thumb abduction/extension with force • Pronator Teres Syndrome • repeated gripping and grasp • tight gripping, turning of tools • forceful flexion with finger flexion and/or elbow extension

  11. Design Principles

  12. Factors to Minimize • Soft tissue, artery, and nerve compression • Grip/Finger/Torque/Push/Pull strength required to perform task successfully • Vibration levels • Temperature changes (+/- 2 degrees) • Repetitive motion • Prolonged performance of task • Prolonged maintenance of “fixed position” • Angle deviation away from “neutral” hand position • Pinching, sharp corners, edges • Cost

  13. Factors to Maximize • General feeling of “comfort” • Adjustability of design • Ease of use • Factors to Consider Depending on Use • Weight of tool • Texturing, gloves, bracing/support, padding • Size of tool and hand anthropometrics • Subgroups: Lefthanders, women, physically impaired, young, elderly • Safety and protection features (e.g. flange, safety latch, plastic guard, etc.) • Material selection – What’s it made of? Why? • Power Specs: Manual vs. powered, Battery vs. plug-in, North American vs. European standards

  14. Shape

  15. Conventional Handle Modified Handle

  16. [Lewis and Narayan, 1993]

  17. Orientation

  18. [Chaffin et al., 1999] Thumb Switch Finger Switch

  19. Size

  20. [Chaffin et al., 1999]

  21. Weight

  22. Bicep Muscle Force Tool + Arm Weight Tool Weight (WT) Tool-to-Elbow Length (L) Added Torque from Tool Weight Total Elbow Torque, T [N-m] T = To + (WT)(L) } To = Net Torque on Elbow without tool Weight of tool may work AGAINST task performance • e.g. torque or moment around arm joints may eventually cause muscle fatigue, etc. Tool Weight (WT)[N]

  23. Arm Weight and Push Force Tool Weight (WT) Required Total Push Force Needed For Task, P [N] P = Po - WT Po = Net Push Force without Tool weight Tool Weight (WT)[N] • Weight of tool may work FOR task performance • e.g. less pushing force required in using a chain saw, electric sander, drill, hammer, etc.

  24. Grip Strength

  25. Vibration

  26. Lower temperature associated with loss of sensitivity, dexterity, and grip

  27. Texturing and Gloves

  28. [Chaffin et al., 1999]

  29. Performance (time to complete) for a task while wearing gloves made from various materials. % time shown in comparison to bare handed performance time (Weidman, 1970)

  30. Sources 1 • Aghazadeh and Mital, “Injuries due to handtools”, Applied Ergonomics, 18(4):273-278, 1987. • Armstrong, An ergonomics guide to carpal tunnel syndrome, AIHA Ergonomic Guide series, American Industrial Hygiene Association, 1983. • Armstrong et al., “Investigation of cumulative trauma disorders in a poultry processing plant”, American Industrial Hygiene Association Journal, 43(2):103-116, 1982. • Chaffin, “Localized muscle fatigue—definition and measurement”, J.Occup.Med., 15(4):346-354, 1973. • Chaffin et al., Occupational Biomechanics, 1999. • Greenberg & Chaffin, Workers and their Tools, 1976. • Hall, Basic Biomechanics, 1999. • Hansson et al., “Vibration in car repair work”, Applied Ergonomics, 18(1):57-63, 1987. • Johnson, “Evaluation of of powered screwdriver design characteristics”, Human Factors, 30(1):61-69, 1988.

  31. Sources 2 • Koradecka, “Peripheral blood circulation under the influence of occupational exposure to hand-transmitted vibration”, In: Proceedings of the International Occupational Hand-Arm Vibration Conference, NIOSH, 1977. • Knowlton & Gilbert, “Ulnar deviation and short-term strength reductions as affected by a curve-handles ripping hammer and a conventional claw hammer”, Ergonomics, 26(2):173-179, 1983. • Lewis & Narayan, “Design and sizing of ergonomic handles for hand tools”, Applied Ergonomics, 24(5):351-356, 1993. • Terrell & Purswell, “The influence of forearm and wrist orientation on static grip strength as a design criterion for hand tools”, Proceedings of the Human Factors Society 20th Annual Meeting, pp.28-32, 1976. • Tichauer, “Ergonomics: The state of the art”, American Industrial Hygiene Association Journal, 28:105-116, 1967. • Tichauer, The Biomechanical Basis of Ergonomics, 1978.

  32. Sources 3 • Wang et al., “Grip strength changes when wearing three types of gloves”, Proceedings of Interface 87, Human Factors Society, pp.349-354, 1987. • Webb Associates, Anthropometric Source Book (Vol.II), NASA Reference 1024, Washington, DC, 1978. • Weidman, Effect of safety gloves on simulated work tasks, 1970.

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