Principles of Ergonomics

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 Ralph Barnes' 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