An Introduction to Hand/Arm Vibration

This tutorial provides an overview of the accepted standards for hand/arm vibration testing and measurement, as well as guidelines for tool designers.

Historical Trends

Hand/arm and whole-body vibration testing are methodologies for studying the way in which vibration affects humans. The Physical Agents (EMF) Directive in Europe started with logging tools, specifically engine-driven saws, as a way to look into the impact on workers of the the tools and machinery they use. In 2002, the EU Vibration Directive was implemented, putting increased emphasis on the testing and effects of vibrations resulting from machinery.

Key Terminology

• Vibration Emissions—The vibration produced by machinery and tools and often relating to the quality of the product
• Vibration Exposure—The effect of machine and tool vibration on the user; the impact on the operator using the tool.

Effects of Vibration on Users

When excessive vibration is experienced by tool operators, they may experience symptoms of TVD (total vibration disorder). The vibration can cause the blood pressure in the hands to drop, resulting in limited blood flow to the fingers. Under current directives and guidelines, tool manufacturers must report tool vibration when the level of hand/arm vibration is greater than 2.5 m/s².

In general, the European (and other) vibration directives are designed to help employers reduce risk of employee injury and liability. The directives help to establish a standard process by:

• Identifying workplaces with vibration exposure
• Establishing realistic (typical) exposure time—For example, an employee that operates high vibration equipment may only do so for a few minutes even though they use that tool during their entire shift—e.g., an impact wrench that is only operated for 1 minute between 10 minute intervals is exposed to 6 minutes per hour x 8 hours per shift = 24 minutes per shift.
• Measuring and calculating the value of actual vibration exposure, also known as A(8)

CEN Standards for Emission from Vibrating Equipment

• A Standard
• B Standard—A standard for general measurement of vibrating devices.
• C Standard—The test code that was used for the vibration test (typically undertaken and provided by the manufacturer of the tool).

Common Vibration Emission Standards and Guidelines

• EN 1033—Measurement of vibration from hand-guided machines
• ISO 8662—Measurement of vibration from non-electrical machines
• ISO 8662-5—Measurement of vibration from concrete breakers and hammers used in construction

Common Vibration Exposure Standards and Guidelines

• ISO 5349-1 (2001)—General requirements and frequency weighting filter details, including information on A(8) levels
  • A(8)—Actual vibration level exposure over an 8 hour (workday) timeframe
    • If A(8) > 2.5 m/s^2, employers must be put into place plans to reduce the vibration level, also called the “action level.”
    • If A(8) > 5.0 m/s^2, employers can be legally liable for damages and injury to workers, also known as the “exposure limit value.”
• ISO 5349-2—Field testing requirements

Currently, there is no generally accepted way to convert the vibration emissions measurement reported by tool manufacturers into vibration exposure. A proposal to standardize this procedure, CEN-TR, is currently under review.

Guidelines for Tool Manufacturers

The goal for tool manufacturers should be to reduce vibrations through better design of tools. In studying the tool, designers should consider the following:

• In general, tools can be regarded as rigid bodies…
• Forces act on that tool…
• And the vibrations are the result of the forces.

Forces that Act on Tools

• Process Independent (tool only)
  • Rotating imbalance
  • Acceleration of pistons
  • Variations in motor torque
• Process Dependent
  • Contact between the tool and the work piece (for example, an angle grinder)
  • Reflected shock waves (for example, hammer)

Design Guidelines and Tips

1. Reduce forces
   • Remove and limit unbalance in rotating parts
   • Design so that reaction forces act on the tool (for example, a chisel) instead of the tool housing
2. Reduce influence of forces
   • Increase mass
   • Increase moment of inertia
   • Decrease distance from center of gravity to rotating unbalance
3. Reduce forces on the hand and arm
   • Isolate support handles
   • Implement mechanical or air springs in handles

About National Instruments

National Instruments Sound and Vibration Measurement Suite, when used with a dynamic signal acquisition device, provides compliance with ISO 5349 testing standards for human weighting filters when measuring hand/arm vibration exposure.

This tutorial was developed with information presented at the SVIB (Scandinavian Vibration Society)
conference, November 22, 2007.

1 ratings | 4.00 out of 5

Print

Reader Comments | Submit a comment »