Ergonomics for senior design 10 3-12

Ergonomics

R.W. Marklin, Ph.D., CPE

Professor, Mechanical Engineering

Oct. 3, 2012

What is ErgonomicsA Primer

R.W. Marklin, Ph.D, CPECertified Professional Ergonomist

Dept. of Mechanical Engineering

Marquette University

Etymology of Ergonomics

Ergo: work from GreekNomos: laws, customsErgonomics is etymologically laws or

customs of workBut we need a less abstruse definition in

order to understand ergonomics in the contemporary world

Definition of Ergonomics

Ergonomics is the science of evaluating and designing products and work environments around the strengths and limitations of the human user in order to:Maximize occupational healthMaximize ease of use Maintain productivity of user

PsychoSocialWork OrganizationWorker SatisfactionMgmt-Worker Rel.

Compensation.

Cognitive FactorsMental workload

Physical FactorsTools and Equipment

Methods of TaskMeasure external

and internal forces (EMG)

Human Operator

Industrial HygieneNoise

Heat/ColdChemicals R.W. Marklin is a

Physical Ergonomist

Three Spheres of Ergonomics

Truck Cab Dimensions

Cab Design

Seat Travel- Forward and RearSeat to Bulkhead DistanceSteering Wheel HeightCab Ceiling HeightPedal LocationHeight between Cab Floor and IP

7

Insufficient Rear Travel

Site Visit vehicle 95th percentile male

modeling by Siemens Jack

Worker’s legs rotated outward

Safety hazard and postural discomfort

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Insufficient Forward Seat Travelavel

Site Visit vehicle 5th percentile female

modeling by Siemens Jack

Worker does have full support from seat back

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Calculating Seat Travel

Accelerator to Seat Ref Point (SRP)

SAE J4004 method for calculating forward and rear seat travel

EPRI 2010 utility workers’ male anthropometry

Gen. pop female anthropometry

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Seat Travel Recommendations:AV / DD Cab

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Seat Travel Recommendations:Pickup Cab

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Seat to Bulkhead Distance

Insufficient distance may not allow driver to recline seatback sufficiently

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Recommendation

Recommended minimum seat to bulkhead distance is 15.7 in.

Seat dimensions taken from database of 27 site visit vehicles

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Recommendation

At least 42 in. height from Seat Ref. Point to cab ceiling

Ht from cab floor to SRP can vary – reason to use SRP

Based on 99th percentile male utility workers

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Pedal Location

Insufficient distance between brake and accelerator Toe stuck under pedal Boot overlaps both

pedals Workers have larger

feet than gen. pop Some workers drive

vehicles without boots

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This cab has sufficient distance between brake and accelerator but not between accelerator and hump.

Recommendation

EPRI 2010 anthropometry study: 99th percentile shoe size was 14D

2 in. clearance added to ½ of boot width

Center of accelerator used to accommodate big boots (overlap with big boots and narrow accelerator)

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Recommendation

99th percentile boot size

Vehicle database used for dimensions and angle of accelerator

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Computer Keyboards

Computer Keyboard Designs

Computer Keyboard Designs

Conventional keyboardSplit keyboardSloped keyboardTilted keyboard

Epidemiology & Keyboards

Tittirandonda, Burastero, and Rempel (1999) summaryConsistent relationship between

computer-related risk factors and MSDs, specifically sustained awkward postures of wrist

This presentation will address how alternative keyboard designs can reduce awkward postures risk factor

How Do MSDs’ Risk Factors Relate to Conventional Computer Keyboards? Posture

Extended wrist Ulnarly deviated wrist

Repetition 3 key strokes per second Up to 50,000 to 100 000 key strokes

per day

Force Minimal forces but exerted many times

Wrist Deviation and Tendons

Cross-Section of Wrist

Trapezium

Flexor digitorum

superficialis tendon

Flexor digitorum

profundus tendon

Pisiform

Flexor pollicis longus tendon

Flexor carpi radialis tendon

Flexor retinaculum Median nerve

(Saidoff & McDonough, 2002)

Biomechanical Consequences of a Deviated Wrist Position

Friction of tendons across the carpal tunnel Requires more muscular effort due to friction and contact forces May lead to tenosynovitis (friction causes irritation of tendons,

leading to inflammation, pain and swelling) May lead to carpal tunnel

syndrome (swelling in the carpal tunnel leads to increased carpal tunnel pressure)

Carpal Tunnel Pressure

Pressure against median nerve in carpal tunnel could cause carpal tunnel syndrome

Pressure against tendons and their sheaths could cause tenosynovitis

Carpal Pressure (mm Hg) = f (wrist flex/ext)

0

10

20

30

40

50

60

70

-60 -40 -20 0 20 40 60

Flexion * Extension

(Rempel et al., 1997)

Split Keyboard

Slant angle of a keyboard Split fixed-angle Split adjustable-angle

10.5° slant

12.5° slant

The slant angle is half the opening angle

Sloped Keyboard

Slope angle of a keyboard Positive slope keyboard Negative slope keyboard

15° slope

-15° slope

Tilted Keyboard

Tilt angle of a keyboard Vertically inclined keyboard

20° tilt

Conventional Keyboard Wrist Deviation

Left hand Wrist Ulnar Dev.

15.0 ± 7.7°

Wrist Extension 21.2 ± 8.8°

Pronation 62.2 ± 10.6°

Right hand Wrist Ulnar Dev.

10.1 ± 7.2°

Wrist Extension 17.0 ± 7.4°

Pronation 65.6 ± 8.3°

Simoneau et al. (1999)

N = 90 touch typists (approx. 60 wpm)Age = 37.8 ± 9.3 yearsExperience = 14.4 ± 8.8 years

Fixed-Angle Split Keyboard

Adjustable-Angle Split Keyboard

Right Wrist Ulnar Deviation

Marklin et al. (2000)

Wrist Extension

Marklin et al., 2000

Summary of Split Keyboards

Split keyboards with opening angle of 20˚ to 25˚reduced ulnar deviation by >10˚Within 2˚ of neutral for rightWithin 5˚ of neutral for left

Reduced wrist factor of ulnar deviationNo decrease in typing speed or accuracy

Recommended Keyboards

Electric Power Industry

Ergonomics Handbooks

EPRI Document #1005199

November 2001


March 2004


March 2005


January 2008


March 2008

Manhole Covers

Removing and Replacing Manhole Covers: Current Work Practice

Manholes provide access to underground vaults and utility corridors

Square: up to 3 ft x 4 ftRound: up to 4 ft in diameter123 to 209 lbs


Hook and chainSteel lifting hook


1st class lever with a magnet


1st class lever with a magnet


2nd class lever

Removing and Replacing Manhole Covers: Problems

High forces on shoulder and trunk muscles – particularly using the hook and chain and steel lifting hook

Removing and Replacing Manhole Covers: Recommended Ergonomic Recommendations

1st class lever with magnet

2nd class lever

Removing and Replacing Manhole Covers: Benefits of 1st class lever with magnet

Based on field study with 32.5 inch 175 lbs coverPeak force with handle attached to 175 lbs

cover: 177 lbfPeak force with 1st class lever: 68 lbf

Removing and Replacing Manhole Covers: Benefits of 1st class lever with magnet

University of Michigan 3D SPPP based on field study with 32.5 in. 175 lb cover:Spinal compression with hook and chain:

over 2800 lbfSpinal compression with 1st class lever and

magnet: < 433 lbfNIOSH safe limit = 770 lbf

Mobile Computers

Laptops in Utility Vehicles

Mobile Computer Laboratory Study

Investigate the effects of different laptop PC locations in a utility vehicle cabBiomechanical effectsPerformance and safety effectsSubjective assessment

amystone

i asked rich and kyle for photos.

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Location on Passenger Seat

On top and in front of passenger seat

Location – Driver Side

Goniometers and EMG

Shoulder Angle

Laboratory Study: Dependent Variables

BiomechanicalBody segment angles

Neck angle (rotation and flexion)Shoulder (abduction and flexion)Elbow (flexion)Wrist (radial/ulnar deviation and flexion/extension)Trunk (rotation and flexion)

Muscle force: EMG activity of major trunk, shoulder and arm muscles

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Laboratory Study: Dependent Variables

Comfort and effortAssessed using ordinal subjective

assessment formsPerformance

Time to complete tasks on PCAccuracy of tasks

PreferenceRank order of placement from worst to bestSelection of best placement

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Left Erector Spinae EMG

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Laptop on and in front of passenger seat (A & B) increases left back muscle force substantially for both tasks

Left Erector SpinaeN=7

L o ca ti o n *T a sk; We ig h te d M e a n s

V e rti ca l b a rs d e n o te 0 .9 5 co n fi d e n ce i n te rva l s

K e yb o a rd

T o u ch scre e n

0 .1 7 5 2

0 .1 0 3

0 .0 4 0 40 .0 6 0 1

0 .1 7 5 2

0 .1 0 3

0 .0 4 0 40 .0 6 0 1

0 .1 8 2 6

0 .1 4 5 8

0 .0 8 8 0 .0 8 7 9

0 .1 8 2 6

0 .1 4 5 8

0 .0 8 8 0 .0 8 7 9

A B C D

L o ca ti o n

0 .0 0

0 .0 5

0 .1 0

0 .1 5

0 .2 0

0 .2 5

0 .3 0

Me

an 0 .1 7 5 2

0 .1 0 3

0 .0 4 0 40 .0 6 0 1

0 .1 8 2 6

0 .1 4 5 8

0 .0 8 8 0 .0 8 7 9

Right Deltoid EMG

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Laptop on and in front of passenger seat (A & B) increases right shoulder force substantially for touchscreen tasks

R ight D eltoidN=22

L o ca ti o n *T a sk; We ig h te d M e a n s

V e rti ca l b a rs d e n o te 0 .9 5 co n fi d e n ce i n te rva l s

K e yb o a rd

T o u ch scre e n

A B C D

L o ca ti o n

0 .0 0

0 .0 5

0 .1 0

0 .1 5

0 .2 0

0 .2 5

0 .3 0

Me

an

Recommended Location of Laptop

Subjective Assessment

Subjects overwhelmingly liked the locations near driver seat

Disliked the locations near passenger seat

Question 3: Median R esponseN=22

4 .0

5 .0

5 .5

2 .0

0 1 2 3 4 5 6

BC

D A

4 .0

5 .0

5 .5

2 .0

Wind Turbines

Wind Turbines – Enormous, Plentiful (>15,000 in US), and Growing

Lakeshore Technical College

135 ft. wind turbine 24 new students each

year 100% placement 1 hour drive from

Milwaukee

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Wind Power Maintenance Tasks

Inspection and maintenanceOil exchange and filtersCheck torque on boltsParts removal and replacement

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Wind Turbine Site Visit

Texas site

Wind Turbine Site Visit

Tasks in Nacelle (box on top to tower)8 ft tall, 8 ft wide, 20 ft long

Muchas Gracias