A Comparison Study A Comparison Study of Impact Hammersof Impact Hammers

Steven G. Chervak, MS, Steven G. Chervak, MS, CPECPE

FHP, 2003 Steven Chervak

Presentation Presentation OutlineOutline

Background Background InformationInformation

MethodologyMethodology ResultsResults ConclusionConclusion

FHP, 2003 Steven Chervak

FHP, 2003 Steven Chervak

BackgroundBackground

Purpose of Project:Purpose of Project:

Evaluate effectiveness of replacing Evaluate effectiveness of replacing current tools with newer, better current tools with newer, better designed tools as related to:designed tools as related to:

- Productivity- Productivity

- Vibration levels- Vibration levels

- Worker’s physiologic demand- Worker’s physiologic demand

FHP, 2003 Steven Chervak

BackgroundBackground Worker Focus GroupWorker Focus Group

Anniston Army DepotAnniston Army Depot Injury recordsInjury records Determine study focus Determine study focus Problematic tool identificationProblematic tool identification

Initial StudyInitial StudyAnniston Army DepotAnniston Army Depot

Tank Disassembly LineTank Disassembly Line

FHP, 2003 Steven Chervak

MethodologyMethodology

FHP, 2003 Steven Chervak

Methodology -Methodology -SubjectsSubjects

11 Volunteer Subjects11 Volunteer Subjects MaleMale Avg. Age: 49.9 yearsAvg. Age: 49.9 years Time at Job: 12.1 yearsTime at Job: 12.1 years

FHP, 2003 Steven Chervak

Methodology - Methodology - ToolsTools

Three – 3/8 Inch Three – 3/8 Inch impact wrenchesimpact wrenches Tool # 1 – New, Tool # 1 – New,

Manuf. AManuf. A Tool # 2 – New, Tool # 2 – New,

Manuf. BManuf. B Tool # 3 – Old, Tool # 3 – Old,

Manuf. CManuf. C

Similar Weight, Shape Similar Weight, Shape & Size& Size

FHP, 2003 Steven Chervak

Methodology – Task Methodology – Task

Remove 4 bolts Remove 4 bolts from wheel guard from wheel guard with with eacheach impact impact hammer/wrench.hammer/wrench. Randomized Randomized

orderorder Bolt tightened Bolt tightened

to 175 ft-lbs. to 175 ft-lbs. prior to removalprior to removal

FHP, 2003 Steven Chervak

Methodology - Methodology - MeasurementsMeasurements

ProductivityProductivity

ElectromyographElectromyographyy

VibrationVibration

FHP, 2003 Steven Chervak

Measurements Measurements ProductivityProductivity

Average Bolt Removal Average Bolt Removal TimeTimeVia accel. Via accel. measurementsmeasurements

FHP, 2003 Steven Chervak

MeasurementsMeasurements

Electromyography (EMG)Electromyography (EMG) Surface ElectrodesSurface Electrodes Band pass filter ( 13 hz – 150 Band pass filter ( 13 hz – 150

hz)hz) Sampled at 200 hzSampled at 200 hz Full wave rectifiedFull wave rectified

FHP, 2003 Steven Chervak

EMG - ContinuedEMG - Continued

Two muscles measuredTwo muscles measured Flexor digitorum profundusFlexor digitorum profundus

Flexes phalanges and Flexes phalanges and handhand

% Maximum Voluntary % Maximum Voluntary Contraction (%MVC) via Contraction (%MVC) via hand dynamometerhand dynamometer

Copyright Spencer, 1987

FHP, 2003 Steven Chervak

EMG - ContinuedEMG - Continued

Two muscles Two muscles measuredmeasured BrachioradialisBrachioradialis

Flexes forearmFlexes forearm % Maximum % Maximum Voluntary Contraction Voluntary Contraction (%MVC) via isometric (%MVC) via isometric contractioncontraction

Copyright Spencer, 1987

FHP, 2003 Steven Chervak

MeasurementsMeasurements VibrationVibration

100 mv/g Triaxial 100 mv/g Triaxial AccelerometerAccelerometer

Sampled at 2000 hzSampled at 2000 hz 1000 hz low pass 1000 hz low pass

filterfilter Root Mean Square Root Mean Square

(RMS) values(RMS) values

FHP, 2003 Steven Chervak

ResultsResults

FHP, 2003 Steven Chervak

Productivity - Bolt Removal Productivity - Bolt Removal TimesTimes

Tool # N Mean Std. Dev. Minimum Maximum1 (New) 11 1.7256 0.3745 1.210 2.3132 (New) 11 1.7300 0.3979 1.060 2.215

3 (Used) 12 7.6574 2.8631 4.408 11.868

Sum of Sq df Mean Sq F Sig.Hypothesis 235.112 2 117.556 48.199 0.000Error 46.34 19 2.439

Tool Performance

ANOVA

FHP, 2003 Steven Chervak

Post Hoc Test for Bolt Post Hoc Test for Bolt RemovalRemoval

SubsetTool # N 1 2

1 11 1.7252 11 1.7303 10 7.657

Sig. 0.995 1.000

Student-Neuman-Keuls

FHP, 2003 Steven Chervak

Surface EMG Surface EMG ResultsResults

% MVC Flexor Digitalis Profundus

ANOVA

Tool # Mean N Std. Dev.1 24.135 10 18.1842 23.266 10 14.6353 19.255 9 8.636

Sum of Sq df Mean Sq F Sig.Hypothesis 992.707 2 496.354 0.673 0.523Error 12541.859 17 737.756

FHP, 2003 Steven Chervak

Surface EMG Surface EMG ResultsResults

% MVC Brachioradialis

ANOVA

Tool # Mean N Std. Dev.1 11.678 11 9.4502 7.682 11 4.7483 5.931 10 3.346

Sum of Sq df Mean Sq F Sig.Hypothesis 138.812 2 69.406 2.503 0.108Error 526.857 19 27.729

FHP, 2003 Steven Chervak

Vibration ResultsVibration ResultsMean Accelerometer Values

Tool # Xrms Yrms Zrms1 7.806 6.589 3.5542 4.409 1.629 1.8963 22.613 45.224 3.599

Significance 0.000 0.000 0.003

FHP, 2003 Steven Chervak

ConclusionsConclusions

New impact wrenches performed New impact wrenches performed significantly better than older tool.significantly better than older tool.

New impact wrenches had less New impact wrenches had less vibration than older tool.vibration than older tool.

Performance of new impact Performance of new impact hammers were similar.hammers were similar.

Physiologic differences were Physiologic differences were negligible.negligible.

FHP, 2003 Steven Chervak

Future workFuture work

Can we optimize tool Can we optimize tool replacement?replacement? ½” impact wrench½” impact wrench Date in serviceDate in service CostCost Service historyService history Vibration level/Production levelVibration level/Production level

FHP, 2003 Steven Chervak

Lessons LearnedLessons Learned

Pilot Study, Pilot Pilot Study, Pilot Study, Pilot Study.Study, Pilot Study. Labs great – no Labs great – no

substitute for realitysubstitute for reality

Heavy tools – look at Heavy tools – look at non-dominant handnon-dominant hand

375 ft/lbs of torque is a 375 ft/lbs of torque is a lot of torque!lot of torque!