GESAC, Inc
Development of Abdomen Compression
Measurement Sensors
T. Shams, N. Rangarajan, J. Rowe, H. Conner
GESAC, Inc
GESAC, Inc
Outline
• Usefulness of compression as injury measure
– some limitations of current methods
• Exploring alternative measurement methods
• Hall sensors
– packaging, calibration, response
• Shape sensors
• Flex sensors
– packaging, calibration, response
• Discussion
• Current work
October 28, 2007
Thirty-Fifth International
Workshop
2
GESAC, Inc
Measuring Abdomen Compression
• Compression measure important in abdomen injury assessment
– Maximum compression, V.C, Vmax.Cmax
– (Cavanaugh, Viano, Rouhana, etc)
• Current measurement methods
– Pressure (Mooney)
– Stringpots (e.g Thor)
– Fluid resistance (Rouhana)
•
Limitations of current methods
– relies on measuring deflections at a points
• may miss location of maximum deflection
• reliability under oblique loading may not be optimum
– no reliable method for measuring in children
October 28, 2007
Thirty-Fifth International
Workshop
3
GESAC, Inc
Exploring Alternative Methods
• Looked at several alternative methods
– Hall sensors
• They can measure relative rotations of a small section up to +/- 40 deg
• Number of sensors can be used to measure deformation of linear strip
– Shape sensor
• Measure displacement at end of flexible beam due to delay in
transmission of light beam
– Resistive flex sensors
• Depends on change of resistivity when a flex sensor is bent
• Can be used to measure average curvature of small sections
October 28, 2007
Thirty-Fifth International
Workshop
4
GESAC, Inc
Hall Sensor-Description
• Sensor is small - < 0.5 cm
• Voltage output proportional
to relative distance between
magnet and sensor
– high level signal
– function of distance or angle
• Easily available
• Can be programmed
– Sensitivity
– Range
– Temperature coefficients
October 28, 2007
Thirty-Fifth International
Workshop
5
GESAC, Inc
Hall Sensor-Mounting & Calibration
• Evaluated sensor response
for various geometries
– Relative location
– Relative angle
• Decided on hinge
mechanism for mounting
sensor & magnet
• Developed calibration fixture
for obtaining calibration data
October 28, 2007
Thirty-Fifth International
Workshop
6
GESAC, Inc
Hall Sensor-Calibration Fit
• Shows good linear fit
between
–25 deg and +25 deg
– Correlation > 0.99
• Shows excellent cubic fit
between –40 deg and
+40deg
– Correlation > 0.9999
• Normally, will program best
range & sensitivity for
individual sensors
• Excellent repeatability
– variation < 0.1%
October 28, 2007
Thirty-Fifth International
Workshop
7
GESAC, Inc
Hall Sensor-Packaging for Abdomen
• Built bands with 3-7 sensors
– Used flexible strips with low
stretchability
– Fit into groove cut into
abdomen foam
• Tested with disk and rod
impactors
October 28, 2007
Thirty-Fifth International
Workshop
8
GESAC, Inc
Hall Sensor-Quasi-Static Response
• In quasi-static loading,
voltage output from sensors
at different locations
reflected local curvature
• Output lagged behind LVDT
but reached peaks at same
time
• Calculated deflection using
calibration values similar to
LVDT
October 28, 2007
Thirty-Fifth International
Workshop
9
GESAC, Inc
Hall Sensor-Dynamic Response
• In dynamic loading, similar
situation
– Initial and final lag
– Computed peak below
external measurement
– Peak also appears more
smoothed out
October 28, 2007
Thirty-Fifth International
Workshop
10
GESAC, Inc
Hall Sensor-Limitations
• Problems
– Proper sizing and mounting of hinges
• Found adhesive that would work with PVC material and Urethane strip
– Mounting of strip
• Strip had lag in following foam deformation
• Tends to move away from foam after impact
• Flexibility of strip requires additional tension-interferes with foam
stiffness
October 28, 2007
Thirty-Fifth International
Workshop
11
GESAC, Inc
Shape Sensor-Description
• Available from Measurand,
Inc (Canada)
– Has processing box
attached
• Tested with angular
calibration fixture
October 28, 2007
Thirty-Fifth International
Workshop
12
GESAC, Inc
Shape Sensor-Calibration & Limitations
•
•
Shows reasonable linear fit
between –90 deg and +90 deg
Limitations
– Requires multiple sensor array
to cover perimeter of abdomen
– Much more expensive
– Requires separate processing
box, especially for high speed
applications
– Previous user experience
indicated special procedures for
using with soft foam substrates
October 28, 2007
Thirty-Fifth International
Workshop
13
GESAC, Inc
Flex Sensor-Description
• Resistive flexible sensor
– Resistive layer painted,
usually on Mylar backing
– Conductive sections painted
on one side
– Resistance proportional to
amount of bending
• Obtained from electronic
stores
– Used in data gloves
– Inexpensive
– Longer strips can be made
October 28, 2007
Thirty-Fifth International
Workshop
14
GESAC, Inc
Flex Sensor-Calibration Procedure
• Calibration
– Using various radii wooden
templates
– Get voltage output as
function of curvature (or
radius)
– End point at location of
solder tabs can cause
problems
October 28, 2007
Thirty-Fifth International
Workshop
15
GESAC, Inc
Flex Sensor-Calibration Fit-1
• Calibration graph
– Each segment appears
fairly linear after initial low
slope
(~ 0.1 (1/in) curvature)
• Linearity depends on
uniformity of conductive
sections
– Better fit over longer
segments
October 28, 2007
Thirty-Fifth International
Workshop
16
GESAC, Inc
Flex Sensor-Calibration Fit-2
• Multi-segment strips show
some variation between
segments
• Quadratic (with flat as zero)
shows best fit
– R2 ~ 0.99
October 28, 2007
Thirty-Fifth International
Workshop
17
GESAC, Inc
Flex Sensor-Preliminary Testing
• Tested using small foam
components
– Horizontal & vertical
orientations of sensors
– Quasi-static
– Impact speeds = 1 – 3 m/s
– Impactor mass = 3 – 5 kg
– External displacement
measured by LVDT
October 28, 2007
Thirty-Fifth International
Workshop
18
GESAC, Inc
Flex Sensor-Preliminary Results
• Preliminary results show
– Peak deflection and peak
time predicted within +/- 5%
– Unloading occurs more
rapidly
– With two strips, the peak
deflections show similar
time histories
October 28, 2007
Thirty-Fifth International
Workshop
19
GESAC, Inc
Flex Sensor-Testing with Infant Dummy
• Testing with Aprica 3.4 kg
infant dummy
– Disk and cylindrical
impactors
– Tested in horizontal and
vertical configurations
– Tested with two or three
strips
October 28, 2007
Thirty-Fifth International
Workshop
20
GESAC, Inc
Flex Sensor-Results with Infant Dummy
• Comparison with LVDT
–
–
–
–
–
Small initial lag
General agreement in time
Peak underestimated
Faster unloading
Two parallel strips show
good agreement
October 28, 2007
Thirty-Fifth International
Workshop
21
GESAC, Inc
Flex Sensor-Offset Testing
• Offset impacts with rod
– Expected variation with
distance
• No internal stringpot to
measure deflection
independently
Offset
October 28, 2007
LVDT
Flex
center
33.7
32.5
+0.5
35.1
21.2
+1.0
38.6
5.7
-0.5
31.3
22.7
-1.0
32.3
6.9
Thirty-Fifth International
Workshop
22
GESAC, Inc
Discussion-1
• Both Hall sensors and Flex sensors show promise as
possible instruments for measuring dynamic
compression
– end conditions need to be addressed
• Hall sensors
– with proper mounting, show good calibration fit (cubic fit) and
repeatability (R2 > 0.9999)
– problem with maintaining contact with abdomen surface
– still need proper procedure for stringing array of sensors into
linear strip
October 28, 2007
Thirty-Fifth International
Workshop
23
GESAC, Inc
Discussion-2
• Flex sensors
– can be obtained as strip- eliminating difficulties in
construction
– calibration fit not as precise as Hall (quadratic fit) - R2 ~ 0.99
– good repeatability
– problems in securely attaching additional wire contacts along
length
– ends tend to rebound faster, making unloading appear faster
– smaller strips ( 4.5 in – 9 in) are appropriate size for child
abdomens
• can be mounted in horizontal and vertical arrangements
October 28, 2007
Thirty-Fifth International
Workshop
24
GESAC, Inc
Current Work
• Selecting optimum length and number of segments
for use in different abdomen sizes including infant
dummy
• Verifying measurements under oblique and offset
impacts
• Improving computation procedure with variable end
conditions
October 28, 2007
Thirty-Fifth International
Workshop
25
GESAC, Inc
Acknowledgment
We would like to thank
Toyota Motor Corporation, Japan
for funding this work
October 28, 2007
Thirty-Fifth International
Workshop
26