a comparison study of impact hammers steven g. chervak, ms, cpe
TRANSCRIPT
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
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
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!