Design and test of a portable X-Ray detector

Dave CorbenPhilips Applied Technologies, EindhovenNoordwijk, 27-September-2007

Contents• Introduction portable X-Ray detector• Way of Working• Concept design• Fem calculations

– Optimisation– Influence of orientation

• Measurements & Testing• Results & Conclusions

Conventional X-Ray

With portable detector

RAD detector panel

ScintillatorDetector matrix

Line driver ICs &

Readout ICs

Top Sealing Glass

Relevant Requirements• Active area 430*350 mm• Thickness ≤ 25 mm• Weight < 5 kg• No cable• Drop height > 0.7 m

Way of Working• Design Principles• Hand calculations • Computer Simulation• Testing

FMEA EvaluateFM’s

Specification(& test method)

(concept) design

Possible failure modes

Serious failure modes

Design Improvements

Test Method

• Drop from specified height onto hard floor– 9 orientations face down– 9 orientations face up

• Fully functional, minor scratches and dents are allowed

Concept Design

• Metal parts magnesium • Base Plate and back cover ribbed and screwed

together to give maximum stiffness

Top cover

Back cover

Base Plate

PCB

Panel

Flex foils

11

Possible Failure Modes for drop

• Accelerations on panel too high (eg crystals pull out of gel)

• Bending of panel too high (glass failure)

• Accelerations on PCB too high (components detach)

12

Possible Failure Modes for drop (2)

• Internal contact front cover to panel eg at overhang.

• Bending of PCB too high (solder connections break)

• Shear force on screws too high

• …

Trade off: Bending vs Acceleration

M

K

h

ωω

⋅=

=

impact

impact

va

vx

ˆ

ˆ

MKf

ghvimpact

==

=

πω 2

2

:Where

Trade off: Bending vs Acceleration (2)

5 kg mass, 1 m drop

0

5

10

15

20

25

0.00E+00 5.00E+05 1.00E+06 1.50E+06 2.00E+06 2.50E+06

Spring Stiffness (N/m)

Max

Def

lect

ion

(mm

)

0

50

100

150

200

250

300

Max

Acc

eler

atio

n (g

)

MK

h

Buffers: The best of both worlds(low accelerations, low bending of detector)

h

x• But…• For ideal buffer

1g . 1m = 100g . xx = 10mm

• For linear springx = 20mm

Shock testing of panel and PCB

• Accelerations up to 500g (with bending prevented) do not damage panel or PCB’s

• No external buffers needed - design housing for maximum stiffness

Optimisation of stiffness(simple parametric fem model)

t_plate & deflections

-14.0-12.0-10.0-8.0-6.0-4.0-2.00.02.04.0

0.00 1.00 2.00 3.00 4.00 5.00 6.00

t_rib [mm]

tplate

maxmiduz55max

FEM calculations based on CAD geometry

Influence of orientation

• Reduces their number and complexity• Based on energy considerations:

– Flat drop: all kinetic energy transformed to strain energy– Angle drop: some energy remains in rotation

• Flat drop on 4 corners is worst case for drop at an angle• Used as basis for simulations and testing

Bending stress vs drop angle

Measurements

9mm8ms (60Hz)

Static Dynamic

Static Stiffness5e5 N/m

0200400600800

1000120014001600

0 1 2 3 4 5 6

dis placem ent [m m ]

load

[N]

5e5 N/m => 50 Hz

Free fall tests

Functional mockup

Results

• Product now survives 75cm drop• Improvements now being implemented, final

result expected to be close to 1m • Weight and thickness within spec• Product launch at the end of this year

Conclusions• The portable detector now survives from a drop

height of 75cm• Design was based on a pragmatic combination

of:– Design Principles– Hand calculations– Computer Simulation– Testing