Principles of Ergonomics

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 and 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.
• Keep the effective weight of the tool low.
• Align the tool center of gravity and the center of the 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.
• 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.
• Tools should weigh less than 9 lbs- 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

Ergonomic Series Articles

Ergonomics In Lean Manufacturing

Physiology
Biomechanics In Workstation Design
Anthropometry
Man-Machine Allocation
Musculoskeletal Disorders
Principles of Ergonomics
Ergo Download

Reference

Lee, Q, Nelson W., Amundsen, A., &  Tuttle, H., Facilities and Workplace Design, Institute of Industrial Engineers, Atlanta, Georgia, 1996.