GESAC, Inc

Development of Abdomen Compression Measurement Sensors

T. Shams, N. Rangarajan, J. Rowe, H. Conner

GESAC, Inc

October 28, 2007 Thirty-Fifth International Workshop

2

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

3

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

4

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

5

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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

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

14

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

15

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

16

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

17

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

18

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

19

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

20

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

21

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

22

GESAC, Inc

Flex Sensor-Offset Testing

• Offset impacts with rod– Expected variation with

distance• No internal stringpot to

measure deflection independently

Offset LVDT Flexcenter 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

October 28, 2007 Thirty-Fifth International Workshop

23

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

24

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

25

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

26

GESAC, Inc

Acknowledgment

We would like to thank

Toyota Motor Corporation, Japan for funding this work