an adaptive 3d machine vision system for electronic

An adaptive 3D machine vision system for electronic components inspection

Department of IE&MYuan-Ze University

Hsu-Nan Yen Du-Ming Tsai

Contents

Introduction

Method

System description

Experimental results

Conclusion

Introduction -Status in electronic industry

light, thin, small and multifunctional electronic products

minify electronic componentshigh-density packaging

3D measurementto ensure reliability

-

Introduction -Some methods for 3D measurement

Laser scanning techniques

X-ray detection methods

Microscope inspection with focus-based methods

Projected fringes with phase shifting techniques


Laser scanning techniquesslow with a point-by-point or line-by-line scan

measuring accuracy is affected by the beam spot reflection and stray light.






X-ray detection methodsrequire expensive equipment

suffer from long measuring time






Microscope inspection with focus-based methodsinherently small effective area of detection






Projected fringes with phase shifting techniquesfull-field 3D measurement fast inspection

high accuracy

Method -Relationship between surface height and phase

General optical geometry of projected fringes method.

• The surface height is determined by

the difference of and .

)],(),([ yxyxk or φφ −⋅=

),( yxrφ is the phase function on the reference plane;

),( yxoφ is the phase function in the presence of object.

),( yxrφ

),( yxh

),( yxoφ

CCDGrating

P0

D

C B AReference plane

θdθp

h(x,y)Object

z

O

)tantan

1(

tan),(

p

d

dACyxh

θθ

θ

+=

A projected sinusoidal fringe image can be expressed as),(cos),(),(),( yxyxIyxIyxI mb φ+=

where k is a constant for a given system setup;

Method -Extracting phase from intensity images

),(cos),(),(]0),(cos[),(),(),(1 yxyxIyxIyxyxIyxIyxI mbmb φφ +=++=

),(sin),(),(]2

),(cos[),(),(),(2 yxyxIyxIyxyxIyxIyxI mbmb φπφ −=++=

),(cos),(),(]),(cos[),(),(),(3 yxyxIyxIyxyxIyxIyxI mbmb φπφ −=++=

),(sin),(),(]2

3),(cos[),(),(),(4 yxyxIyxIyxyxIyxIyxI mbmb φπφ +=++=

−−

= −

31

241tan),(IIIIyxφ

Chooseπ/2 as phase shifting increment and adopt four-step phase shifting method.

[ ])(),(cos),(),(),( tyxyxIyxIyxI mbn δφ ++=

and can be obtained by using phase shifting technique.

where )(tδ is the introduced phase shift.

),( yxrφ ),( yxoφand

),( yxrφ ),( yxoφ

The fundamental formula of phase shifting technique is

System -Complete layout

PC

LCD Control Interface

PrecisionTranslation

Stage

Lens 2 Lens 1LCD Panel

CCD

Cool Light Source

Optical Bench


PC



Stage


CCD

Cool Light Source

Optical Bench

cool light source and lens 1

supply the collimated white light


PC



Stage


CCD

Cool Light Source

Optical Bench

LCD panel

generate transparent sinusoidal gratingshift grating with accurate phase increment


PC



Stage


CCD

Cool Light Source

Optical Bench

lens 2

focus the image of sinusoidal grating


PC



Stage


CCD

Cool Light Source

Optical Bench

precision translation stage

place the object under inspection


PC



Stage


CCD

Cool Light Source

Optical Bench

CCD camera

capture the projected fringe patterns

System -Digital phase shifting

PC



Stage


CCD

Cool Light Source

Optical Bench

phase shifting is 0

I1(x,y)


PC



Stage


CCD

Cool Light Source

Optical Bench

phase shifting is π/2

I2(x,y)


PC



Stage


CCD

Cool Light Source

Optical Bench

phase shifting is π

I3(x,y)


PC



Stage


CCD

Cool Light Source

Optical Bench

phase shifting is 3 π /2

I4(x,y)

different fringe periods

different phase-variation directions

different grating patterns

easily changed fringe periods,phase-variation directionsand grating patterns

accommodate the topography and reflectanceof various electronic components on PCBs

avoid phase ambiguityreduce overexposure areaincreasing measuring speed

System -Adaptive projection

Experiment -A 1mm gauge block

(a) The 1mm gauge block. (b) The deformed sinusoidal fringes image

of the 1mm gauge block.

(c) The 3D surface profile of the 1mm gauge block.

mean step height is 1.03 mmstandard deviation is 0.04 mm

Experiment -A solder joint on the PCB

(a) A solder joint on the PCB. (b) The deformed sinusoidal fringes image

of the solder joint on the PCB.

(c) The 3D surface profile of the solder joint on the PCB.

Experiment -A sample BGA-joint

(a) The sample BGA-joint. (b) The deformed sinusoidal fringes

image of sample BGA-joint.

(c) The 3D surface profile of the sample BGA-joint.

Full-field 3D measurement system with cost-effective equipment.

Efficient and effective in 3D inspection for small electronic components.

System resolution can be considerably improved by adopting a higher resolution LCD panel, image grabber and CCD.

Conclusion

an adaptive 3d machine vision system for electronic

Documents