Transcript Handtools Extend the capability of the hand Selection criteria:

Handtools
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Extend the capability of the hand
Selection criteria:
 What
the tool can do
 How the tool is used
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Guidelines
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1: Use Special-Purpose Tools __________________
2: Design Tools to Be Used by Either Hand
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3: Power with Motors More Than with Muscles
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4: Use the Proper Grip __________________
5: Make the Grip the Proper Thickness, Shape, and
Length __________________
6: Make the Grip Surface Smooth, Compressible, and
Nonconductive __________________
7: Consider the Angles of the Forearm, Grip, and Tool
8: Use the Appropriate Muscle Group
__________________
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Guideline 1: Use Special-Purpose Tools
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Benefit: Performs well tasks that are repeated many
times/week
Costs: Capital, maintenance, utility
Analysis:
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Tool Selection
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Estimate years of use and usage/year
Divide total cost by usage
Compare to savings
Whether a tool is expensive depends on a detailed analysis,
not just capital cost.
Benefits include savings beyond just labor savings (capability,
quality, etc.)
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Handtool Selection Steps
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2.
Do a job analysis.
Identify tool-use issues:
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Operating forces
Repetitions per minute or per shift
Postures
Select the right tools.
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Guideline 2: Design Tools to Be Used
by Either Hand
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The tool should be in the user’s preferred
hand.
Strength, dexterity, and performance are
greater for the preferred hand.
Benefits:
 Includes
the 10% of the population that is left-
handed.
 Allows nonpreferred hand to be used when the
preferred hand is engaged or resting.
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Handgrip Strengths
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Gloves
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Protect the hand against abrasion, impact,
chemicals, heat, cold, cuts, infection,
vibration.
May decrease manual dexterity and increase
assembly time.
Decrease force grip.
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Guideline 3: Power with Motors More
Than with Muscles
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Mechanical energy is 10 to 1000 times cheaper than
human.
Motors extend capability and do not fatigue.
Motors permit a larger percent of workforce to do the
job.
Reducing Hand–Arm Vibration Syndrome
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Use a process with zero or low operator vibration.
Use equipment with low levels of vibration.
Use equipment with vibration-isolated handles.
Avoid resonance.
Furnish vibration-isolated gloves.
Encourage workers to follow VS-reducing practices.
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Guideline 4: Use the Proper Grip
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Power grip
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Tool handle perpendicular
to the forearm axis.
Direction of force:
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Semipower grip
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Precision grip
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About 20% strength of a
power grip.
Internal (table knife) or
external (pencil) precision
grip
Forearm or tool may be
supported
Fingers act as a group but
thumb position changes.
Oblique or hook grip
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Parallel to forearm
At an angle to forearm
Applied as torque about
forearm
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Hook grips are preferable
to pinch grips.
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Examples
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Guideline 5: Make the Grip the Proper
Thickness, Shape, and Length
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Hand Sizes
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larger with gloves.
 Tend to be larger for men than for women.
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Grip Diameter
 For
power grip, 35 mm to 45 mm is optimal.
 For precision grip, use 9.5 mm to 12.7 mm.
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Grip Shape
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Section Perpendicular to Grip Axis
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Section Along Tool Grip Axis
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Keeps tool from moving forward and backward in hand.
Allows force exerted along tool axis to be greater.
Can act as a shield.
Length
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Prevent rotation and slippage.
Use thumb conoid or noncircular cross-section.
Improve coefficient of friction of handle.
For power grip, all fingers must make contact.
For external precision grip, shaft must be supported.
For internal precision grip, tool must extend past palm but not
as far as wrist.
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Guideline 6: Make the Grip Surface
Smooth, Compressible, & Nonconductive
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Smoothness reduces pressure points.
Compressibility minimizes pressure on the hand.
Nonconductivity reduces heat and cold problems
and risk of electric shock.
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Guideline 7: Consider the Angles of the
Forearm, Grip, & Tool
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Angle
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Clearance
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Keep the wrist in neutral position.
Best angle varies with posture.
Consider changing the job to improve angle.
Consider pistol-grip or bent tools.
Increase distance from hot surfaces to reduce burns.
Provide shield from heat.
A narrow neck reduces heat transfer.
Avoid pinching risk with repetitive-use tools.
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Examples
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Guideline 8: Use the Appropriate
Muscle Group
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Muscle Direction
 Strengths
and ranges of motion differ.
 Consider normally-open tools.
 Give muscle something to push against.
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Muscle Size
 Consider
moment arm.
 Provide power grip.
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Guideline 8 (cont.)
Use the Appropriate Muscle Group
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One versus Many
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Rotate Inward
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Right hand and arm can rotate 70º clockwise, 150º
counterclockwise.
Muscle Time
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Use fingers in combination.
Pinch types vary greatly in strength.
Consider trigger strips instead of buttons.
Consider alternate types of triggers.
Reduce time the muscle is used.
Use clamping tools, locking triggers, discrete controls, straps.
Consider guides or funnels for positioning.
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