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Principles of Ergonomics

Simple Rules for Most Situations 

These principles condense ergonomics into a few simple rules. They are not all-inclusive and do not substitute for in-depth knowledge or common sense. These principles are a natural complement to Principles of Motion Economy

1.0 Extreme Joint Movements

  • Alter the tool or control- bend the tool or handle instead of the wrist.
  • Move the part- rotate the part in front of the worker to keep the wrist straight.
  • Move the Worker- change the worker's position relative to the part.
  • Avoid reaching above shoulder level.
  • Avoid reaching behind the body.
  • Keep elbows close to the sides.
  • Place the work about 2"-4" below the elbow when standing or seated in an erect posture.
  • For precise or delicate tasks, place the work surface 4"-8" above elbow height.
  • For heavy manual assembly, place the work surface 4"-5" below elbow height.
  • Start your design from the working point where the hands spend most of their time.

2.0 Excessive Force

  • Keeping cutting edges sharp and tools well maintained.
  • Spread Force- Alternate hands, use levers instead of buttons.
  • Increase Mechanical Advantage- Use stronger muscle groups and long handles.
  • Use jigs and fixtures whenever possible.
  • Select gloves carefully. They can reduce grip strength up to 15%.

3.0 Repetitive Movement

  • Task Enlargement- Give workers larger and more varied tasks.
  • increase cycle time. 
  • Mechanization- Use special tools with ratchets or power drivers. Automation- Allocate repetitive motions to machines. 
  • Give the operator a neutral posture. 
  • Allow variation of method to prevent a static posture for extended periods.
  • Permit several working positions 
  • Re-sequence jobs to reduce repetition 

4.0 Physiology

  • Allow self pacing of work when possible.
  • Allow frequent rest for most active muscles.
  • Start new employees at a slower rate.

5.0 Hand Tools

  • Provide handles.
  • Design For minimum muscular effort.
  • Power with motors more than muscles.
  • Bend the tool and not the wrist.
  • Align tool center of gravity with center of grasping hand.
  • Use pistol grips for a horizontal tool axis.
  • Use straight grips for a vertical tool axis.
  • Use trigger levers rather than buttons.
  • Design special use tools if needed.
  • Design tools for use by either hand. (11% are left-handers)
  • Use A Minimum handle length of 4".
  • Use grips which accommodate different size hands.
  • Use non-porous, non-slip, & non-conductive grips.
  • Spring load pliers and scissors.
  • Keep the tools lightweight-- 9 lbs Absolute Max.
  • Suspend heavy/awkward tools.

6.0 Position

Use a standing position when:

  • Knee clearance is unavailable.
  • The operator lifts more than 10 pounds.
  • There are high, low, or extended reaches.
  • Operator exerts downward forces- wrapping and packing.
  • The job requires mobility.

Use a sit/stand position when: 

  • Repetitive operations have frequent reaches beyond zone 1.
  • Operator performs sitting and standing tasks.
  • Task requires prolonged static effort.

Use a sitting position when:

  • Items for a repetitive, short cycle are in seated workspace.
  • Hands work less than 6" above the surface.
  • Large force is not required.
  • Handling weight is less than 10 lbs.
  • Task includes fine assembly or writing.
  • Operator needs stability and equilibrium.
  • Task requires precise foot control.
  • Operator has extended time in a fixed position

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