Dept. of Biomedical, Industrial, & Human Factors Engineering 1 Skilled Work Usually hand and finger work Coordinated muscle activity Precise movements Learning is 2 phase process Learning movements-conscious control Adaptation of organs involved From conscious to automatic Gradually eliminate unnecessary muscle & decrease energy requirements

Dept. of Biomedical, Industrial, & Human Factors Engineering 2 Skilled Work Phase I Training Short training sessions Requires high concentration Split job into separate components Set performance expectations for most difficult components Practice important components alone and later put in sequence Strict control and good examples Avoid bad learning habits Young people: learn by example Older people: learning depends more on visual aids

Dept. of Biomedical, Industrial, & Human Factors Engineering 3 Skilled Work Phase II: Body Adaptation Gradual changes in muscles and other organs Build muscle strength Reduce internal friction Eliminate connective tissue and fat Develop sensitivity of neural pathways (reflex arc) Maximum Control of Skilled Movement Max speed of manual operation is in front of the body, elbows at side, and 90 degree elbow angle Best working metabolism with shoulder abducted 8-23 degrees Precision of movement Outward movement more precise Speed max at 45 degrees to right with right hand Lowest oxygen consumption 60 degrees from sagittal Decreses as distance increases Highest precision and fastest movement if forearm the primary limb

Dept. of Biomedical, Industrial, & Human Factors Engineering 4 Hand Tool Design Tools are useless by themselves Tools link workers with their job Tools extend the capabilities of the worker Optimal tool design involves: anthropometry anatomy functional considerations mechanical considerations

Dept. of Biomedical, Industrial, & Human Factors Engineering 5 Hand Tool Design Hand Grips: poor design can lead to poor performance and injury Max grasp force quadrupled by changing from finger grasp to whole hand Finger power maximized when bent slightly upwards (dorsal flexion) Grasp power (& skill) reduced if hand bent downward or turned to side Ulnar/radial deviation reduces rotational ability 50 percent and may inflame tendons if repeated Grip Guidelines Shape handle for grip assist Distribute forces across hand Palm not suitable for stress concentration Wider and cushioned handles all for wider area to bear resultant forces Add stops to prevent tool slippage

Dept. of Biomedical, Industrial, & Human Factors Engineering 6 Hand Tool Design Design of hand grips Cylindrical,  100 mm long, effective up to mm thick Guidelines Grip Consider hand clearance for optimal grip span If too small or too large, forces can’t be applied (~7.5 cm measured at center of hand best) Strength (N) Grip Span (cm)

Dept. of Biomedical, Industrial, & Human Factors Engineering 7 Hand Tool Guidelines Guidelines Grip Consider finger clearance Use analysis of how tools is used and placement of hands and fingers Finger anthropometry Minimizing concentrated stress over soft tissue Palm Fingers Protect hand from external energy Heat, cold Vibration Electric shock

Dept. of Biomedical, Industrial, & Human Factors Engineering 8 Hint and Equipment for Max Skill 1. Manual operations: elbows lowered and forearm angle degrees 2. Delicate work: raise working field to visual field, support forearm 3. Skilled operations with minimize force (heavy force more difficult to control) Avoid imposing static stress at same time 4. Improve concentration on manual operations Support work, foot pedals, chutes and conveyors Try prevent doing multiple things at same time 5. Arrange operations in rhythmic sensible sequence 6. Allow free rhythm rather than imposed pace Less energy, motor control easier, reduced fatigue, less monotony & boredom Too slow requires support, too fast creates nervous stress 7. If using both hand, work field should extend little as possible to side (best visual control), symmetrical motion (begin and end together)

Dept. of Biomedical, Industrial, & Human Factors Engineering 9 Hint and Equipment for Max Skill 8.Forearms and hands at most skillful in precision and speed if take place in degree arc to each side For grasping & working – optimum is 2/3 of maximum reach 9.Horizontal movement easier than verticle control Circular easier than zig zag Each operation should end in position to start next one 10.Handle shaped to fit hand and operate when hand held in line with forearm

Dept. of Biomedical, Industrial, & Human Factors Engineering 10 HT Guidelines Maintain straight wrist (neutral position) Use gloves with caution Extra clearance required Forces applied are less than bare hand Safety hazard – caught in rotating parts Prevent tool slippage during use Flat metal and smooth plastic tool handle can slip Best – compressible rubber hadles that do not absorb liquids and oils Avoid repeated finger activities Finger not used to open or close a tool, use a spring Trigger mechanisms should use multiple fingers to minimize trigger finger syndrome Minimum static loading on hand & arms No heavy tools for extended periods Extended use – tool not to exceed 0.5 kg CoG close to hand to minimize slipping & turning during use Elbows close to body & not elevated when in use