Are DHM and MOCAP reliable and valid for Ergonomics?

Transcription

1 Are DHM and MOCAP reliable and valid for Ergonomics? Leo Tinghao Wu 1,4, Vincent G. Duffy 2,4, Keith White 3, John A. McGinley 4 1. Rehabilitation Institute of Chicago 2. Industrial Engineering Department, Purdue University 3. Lennox International Corporation 4. Center for Advanced Vehicular Systems, Mississippi State University

2 TABLE OF CONTENTS 1. Literature 2. Experiment 3. Results 4. Conclusions 5. Discussions 2

3 LITERATURE Virtual Build Ford Mustang Brazier, Julie, 2003 THE CAR THAT JILL BUILT: A CASE STUDY OF THE 2005 MUSTANG 3

4 Virtual Build Structure Schema by Chaffin 2005 LITERATURE INPUTS OUTPUTS Environment Population data Task Motion Capture files or/and Motion Prediction models Digital manikin motion Ergonomics Assessment Result 1. Fit-Interference 2. Sight Lines 3. Task Times 1. Strength 2. Balance 3. Endurance 4. Injury Risk 5. Discomfort System structure (Chaffin, 2005) 4

5 LITERATURE Reliability The extent to yield the same results on repeated trials. (Merriam Webster, 2002) Test-retest reliability Over-time performance Intra-Class Correlation (ICC) Validity The extent that measure what it supposed to measure. (Carmines, 1979) Criteria-related validity ICC (0.8,1.0] (0.6,0.8] (0.4,0.6] (0.0,0.4] Classification of ICC Meaning Excellent Good Moderate Poor Notes Perfect match Relative high agreement Low reliability, possible being improved No or few correlation A Valid measure must be Reliable. (Hager, 2003) 5

6 Subjects: EXPERIMENT 36 participants, recruited from MSU campus Age:19 48; 23 males, 13 females Stature:152cm 192cm, mean 173.5cm Screen for MSD history and Motion Sickness. Instruments 8-camera motion capture system by Motion Analysis Company UGS Jack v4.0 DHM & Ergonomics Software 5DT Head Mounted Display Physical Mockup 6

7 EXPERIMENT Motion Capture Head Mounted Display Ergonomic Assessments Virtual Environment VE eye view Subject

8 8 EXPERIMENT Reaching Pushing Destin. Origin. Side Destin. Origin. Front Grand Score Rot. Flex. RWL Elbow Torque Shoulder Torque Trunk Torque RULA Static Strength Prediction 91 NIOSH Equation Task Ergonomics Assessments

9 Hypotheses Validity EXPERIMENT 1. The mean 1991 NIOSH lifting equation RWL value of Virtual Build equals to criteria value. H0: RWL =criteria value H1: H0 is false 2. The environment of Virtual Build has no significant effect on ergonomic assessments. H0: µ_real = µ_virtual H1: H0 is false Reliability 1. For all ergonomics assessments, the test-retest reliability of Virtual Build is greater than 0.8. ( Excellent reliability) 9

10 RESULTS Reliability index ( total 17 scores) DHM+MOCAP+Mockup All > 0.8 DHM+MOCAP+VE Three < 0.8 Reliability Score ( ICC) Real Env. Virtual Env. 10 Reach RULA Pushing Elbow Torq. Reliability Score(ICC)) 0 lb Front NIOSH RWL 1 lb Front NIOSH RWL 20 lb Front NIOSH RWL 1 lb Side NIOSH RWL 0 lb Front Flex. Torq. Org. 0 lb Front Flex. Torq. Dest. 1 lb Front Flex. Torq. Org. 1 lb Front Flex. Torq. Dest. 20 lb Front Flex. Torq. Org. 20 lb Front Flex. Torq. Dest. 1 lb Side Flex. Torq. Org. 1 lb Side Rot. Torq. Org. 1 lb Side Flex. Torq. Dest. 1 lb Side Rot. Torq. Dest. Pushing Should Torq.

11 RESULTS NIOSH Equation RWL Manual measurement and calculation: RWL lb T test H0: RWLij = DHM+MOCAP+Mockup : Can not reject H0 for lifting tasks with box DHM+MOCAP+VE : Can not accept H0 Integration Level 0 lb Front 1 lb Front 20 lb Front 1 lb Side DHM + MOCAP + mockup t = 4.35 p < t = 0.35 p = t = p = t = p = DHM + MOCAP + VE t = p < t = p < t = p < t = p < p < 0.05, Can not accept H0 11

12 RESULTS Static Strength Prediction Task : Original/Destination Position One- way ANOVA One factor: Env. (2) Dependent variable: Trunk torque (Nm) Environment has significant effect on trunk flex. Torque at original 0 lb Front 1 lb Front 20 lbs Front 1 lb Side Trunk Flex./Ex Trunk Flex./Ex Trunk Flex./Ext. Trunk Flex./Ext. Trunk Rotation Original Posture F = p <0.001 F=51.79 p <0.001 F= p <0.001 F= p < F= 0.88 p = Destination Posture F = 3.84 p = F=3.73 p =0.055 F= 3.39 p =0.067 F= 2.28 p =0.156 F= 2.19 p = p < 0.05, Can not accept H0 12

13 RESULTS Static Strength Prediction Pushing Task : One- way ANOVA One factor: Env. ( 2 ) Dependent variable: Shoulder & Elbow torque ( Nm) Environment has no significant effect on shoulder torque. Pushing Task Shoulder Torque Elbow Torque ANOVA F = 3.27 p = F = p =0.535 Rapid Upper Extreme Assessment(RULA) Reaching Task : General Linear Model One factor: Env. ( 2 ) Dependent variable: RULA grand score Environment has no significant effect on RULA grand score Chi-Square = 0.02 Pr > ChiSq =

14 CONCLUSIONS Reliability 1991 NIOSH Equation assessment DHM+MOCAP+Mockup : Excellent DHM+MOCAP+VE : Good or Excellent Static Strength Prediction assessment DHM+MOCAP+Mockup : Excellent DHM+MOCAP+VE : Good or Excellent Rapid Upper Extreme Assessment DHM+MOCAP+Mockup : Excellent DHM+MOCAP+VE : Excellent Generally DHM+MOCAP+Mockup are Excellent reliable, DHM+MOCAP+VE has place for improvement in reliability 14

15 CONCLUSIONS Validity 1991 NIOSH Equation assessment DHM+MOCAP+Mockup : valid if lifting with box, weight does not matter DHM+MOCAP+VE : invalid Perceptual feedback is important Additional feedback is needed for DHM+MOCAP+VE Environment matters Depends on assessment tools. 15

16 Real vs. Virtual SSP is based on posture DISCUSSION DHM+MOCAP+Mockup vs. DHM+MOCAP+VE Origin lifting position: trunk torque significant different Destination lifting position: trunk torque no difference task: Origin position task: Destination position Real Virtual Real Virtual 40 of Field-of-View vs. 160 to

17 DISCUSSION Limitation Two trials in one time session Future work Two time sessions Bigger field-of-view VE equipment Add more feedbacks Using dynamic ergonomic assessments 17

18 Questions & Comments 18