Biomechanical Considerations In Machine Control and Workplace Design

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Chapter 10

• Biomechanical Considerations In Machine Control
  and Workplace Design

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Introduction

• Biomechanical factors to consider in design or
  redesign of
• machines
• workplace lay-out
• Intervene to reduce (eliminate) movements that
  are
• frequent
• sustained
• awkward

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Workplace

• Location where a person performs a task for a
  relatively long period of time
• unloading
• assembly
• typing

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Localized musculoskeletal injury in industry

• Frequent repetition of activity (gt several weeks)
  
• gt chronic pain tissue degeneration
• several weeks?? real estate agent DOMS
• Most VOLITIONAL loads are sub-maximal
• fatigue gt mechanical damage
• overstress of muscle
• prolonged poor nutrition
• muscle pump

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Muscle Endurance Guideline

• Muscle activity can only be maintained for
  sustained or frequent exertions by
• maintaining low contractile force
• providing adequate rest periods

and/or
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Guidelines for Workplace and Machine Control
Layout

• If frequent or sustained muscle exertions are
  required
• minimize the external load required
• avoid unnatural (extreme) postures

Torque Force x MA
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Considerations for Workplace Design

• Adapt workplace so that most people can safely
  and effectively perform their tasks
• low risk of trauma
• low risk of overuse
• Adaptable to all who will work there

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Shoulder

• Ball-and-socket joint
• Stability from muscles
• Potential for long resistance MAs
• Relatively short muscle MAs

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Common shoulder injury
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Shoulder

• Arm out from side (abduction or flexion) results
  in discomfort fatigue
• increases muscle activity in a complex way

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Shoulder

• Arm out from side results in discomfort fatigue
  
• Effect of hand held load
• interacts with arm position to affect time until
  muscle pain onset

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Shoulder

• Arm out from side results in discomfort fatigue
  
• Effect of hand held load
• interacts with arm position to affect time until
  muscle pain onset

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Muscle activity with abduction
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Shoulder guideline

• Deviation lt than 35 from midline

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Shoulder guideline

• Deviation lt than 35 from midline
• Low loads (less than 0.4 kg 1 lb)
• Short time periods
• Short duty-cycles
• lt 20 /min

time inversely proportional to intensity
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Useful environment modifications

• Use a padded forearm support
• Why??

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Useful environment modifications

• Use a padded forearm support
• Use a tool balancer
• Why?

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Useful environment modifications

• Use a padded forearm support
• Use a tool balancer
• Work surface to support tool piece, individual
  slides to complete work
• ie routers, sanders
• boards

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Elbow

• Work involving forearm rotation should be
  performed with the elbow flexed
• affects MAof biceps brachi to pronation

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Elbow

• Work involving forearm rotation should be
  performed with the elbow flexed
• NOT JUST SCREWDRIVERS
• Power tools create torques
• Eliminate reaches ACROSS surfaces
• rotate the surface allows
  worker to walk around

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Neck/head postures affecting/affected by work

• Sit with a 10-15 degree backward torso
  inclination
• Why???

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Neck/head postures affecting/affected by work

• Sit with a 10-15 degree backward torso
  inclination
• Avoid neck flexion

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Neck/head postures affecting/affected by work

• Sit with a 10-15 degree backward torso
  inclination
• Avoid neck flexion
• chair
• worksurface
  height inclination

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Bring the work surface to the worker.
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Neck/head postures affecting/affected by work

• Sit with a 10-15 degree backward torso
  inclination
• Avoid neck flexion
• chair
• worksurface height inclination
• work area about 5 cm below elbow
• standing or seated
• temporary jigs to hold material????

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Adjustable work surfaces
Note height, width and tilt adjustments
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Biomechanical considerations in design of VDT
workstations

• Adjustable to the individual
• Typical
• writing desk
• non-tower computer
• monitor on top of computer
• Either too high or too low

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VDT Guidelines

• Eyes 10-15 below horizontal
• arms supported (arm rests)

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VDT Guidelines

• Eyes 10-15 below horizontal
• arms supported (arm rests)
• wrists neutral (cushioned pad)

Ergonomic Keyboards
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VDT Guidelines

• 10-15 below horizontal
• arms supported (arm rests)
• wrists neutral (cushioned pad)
• Typical seating guidelines
• feet flat on floor
• knees hips level
• adequate backsupport
• Visual State Farm Checklist

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