Steven Fischer - the 11th annual Human Factors IUW 2010
1. The Three-Dimensional Hand Force
Prediction Model (3DHFPM):
A method for predicting maximal and sub-maximal
exposure thresholds in the workplace
Steven L Fischer, Clark R Dickerson and
Richard P Wells
University of Waterloo, Canada
2. Overexertion occurs when the load, whether
lifted, carried, pushed, pulled or otherwise
handled, exceeds the limits of the human joint
system doing the work1.
Overexertion – It is a problem
1Wisha-training.lni.wa.gov/training/presentations/Overexertion.ppt
2Workplace Safety and Insurance Board, Ontario, Canada - 2008
1 in 4 lost time claims
are related to
overexertion2.
3. Overexertion – Why it is a problem
Exceed a maximum
capacity threshold limit3
Exceed a sub-maximal
capacity threshold limit3
Threshold Limit
Threshold Limit
3McGill, 1997
4. Overexertion – How we avoid it
Measure empirically or
predict using 3DSSPP ™ 4
Measure empirically or use
Liberty Mutual Tables™ 5
Threshold Limit
Threshold Limit
4Chaffin, 1997
5Snook and Ciriello, 1991
5. A thought experiment
Balance, friction and
joint strength can all
act to limit exertion
capacity6,7.
Can we predict the
limiter?
Can we predict the
exertion capacity at
that limit?
?
?
?
?
6Grieve, 1983
7Kerk et al., 1998
6. Overexertion – Better tools?
Predict the
limiting
factor
Predict the
maximum
capable
exertion
Predict the
psycho-
physically
acceptable
exertion
8. The 3DHFPM – How it works
Inverse static linked segment
model
Joint moments
Normal force
Center of pressure location (COP)
msegment g
+z
+y
+x
Fzprox
Fyprox
Fxprox
Fzdist
Fydist
Fxdist
Mdist (Mxdist, Mydist, Mzdist)
Mprox
rdist
rprox
9. The 3DHFPM – How it works
Probabilistic estimation of limiting factors
25. Impact of COP calculation
X = projection of the COM
O = COP calculated using 3DHFPM
O = COP calculated from force place
Medial push Pull
COPx typically overestimated by 4% relative to force plate COP
COPy typically overestimated by 5% relative to force plate COP
Editor's Notes
Slide Purpose: To illustrate the continued influence of overexertion injuries in the workplace – more than 1 in 4 lost time claims in Ontario is related to overexertion.
Slide Purpose: To illustrate the how an overexertion injury can occur at a maximal or sub-maximal threshold.
Slide Purpose: To illustrate the how an overexertion injury can occur at a maximal or sub-maximal threshold.
Slide Purpose: To discuss the importance of having some predictive ability to understand what can be done in order to determine what should be done.
Currently three methods have been published to enable designers / ergonomists to predict hand force capability or at least the influence of certain hand forces (3DSSPP)
Slide Purpose: To highlight the current interface for the 3DHFPM – focusing on the required inputs and the resultant output capacity
Slide Purpose: To highlight the key model output features and to elaborate on the potential impact this information could have for a decision maker.
Slide Purpose: To thank my PhD funding sources
With a 9 minute talk and 6 minutes for questions I may have an opportunity to respond to questions by presenting some of the evaluation data.
Slide Purpose: To highlight the predictive capacity of the model using a subset of three participants
Slide Purpose: To highlight the predictive capacity of the model using a subset of three participants
Slide Purpose: To demonstrate the difference in COP calculated top-down versus bottom-up using a force plate