D4操作手册.pdf - 第22页

22 Vision Sensor Technology PCB Position Recognition Description Different fiducial shapes prove to be op timal depend- ing on the co ndition of the surface. Particularly ad vis- able for bare copp er surfaces with litt …

Vision Sensor Technology

PCB Position Recognition

Technical data

PCB fiducials

Local fiducials

Library memory f.

recognition of

bad panels

up to 3 (subpanels and multiple

panels)

up to 6 for the Long board option

(Optional PCB fiducials are output by

the optimization.)

up to 2 per PCB (may be of different

type)

up to 255 fiducial types per subpanel

Image analysis Edge detection method (Singular fea-

ture) based on grayscale values

Lighting method Front lighting

Fiducial recogni-

tion time

0.1 s

Field of vision 5.78 x 5.78 mm

Camera’s field of view

Pixel

Ink spot, e.g. square

Evaluation window

Geometrical Alignment

The size of the fiducial is pro-

grammed at the station com-

puter. From this time on form

and size of the fiducial is

defined and known.

With these data the PCB

vision module is able to

search and recognize the

fiducial at the predefined

position on the PCB or ceram-

ic substrate without further

assistance. For this reason it

places several small evalua-

tion windows at the assumed

border of the fiducial. Within

these evaluation windows

the vision system looks for

contrast transitions between

bright and dark. After finding

such contrasts the actual

position of the fiducial can be

assigned by comparison with

the predefined – and thus

known – shape and size.

The analysis operations can

be used to determine any off-

set with respect to the DE-

SIRED position in the X and Y

directions and the angular

position. Alternatively, a fidu-

cial may be taught as a pat-

tern.

Additional functions of the

PCB vision module are recog-

nition of the position of the

feeder modules and ceramic

substrate (optional) and

recording of the machine

data including mapping.

The bad board detector

(GOOD/SCRAP scan) is also

moved over the ink spot

using the PCB vision module.

Description

SIPLACE has a number of

vision modules and a central

vision system to evaluate the

recorded image data ensur-

ing high placement accuracy.

At the machine's X-gantry

the PCB vision module is

mounted. It is used to find

the PCB's positioning-offsets

within the conveyor system.

This vision module is also

required to measure the

machine origin and/or the

feeder module positions on

one side of the table.

Each vision module consists

of a single CCD camera with

integrated lighting and

optics. The offsets in the

position of the PCBs are

determined with the help of

at least two but generally

three reference fiducials on

the PCB. When the PCB

arrives at the placement area

the positioning system with

its PCB vision module moves

to the programmed fiducial.

The edge detection method

allows to choose predefined

fiducials from a menu (e.g.

cross, circle, square).

Vision Sensor Technology

PCB Position Recognition

Description

Different fiducial shapes

prove to be optimal depend-

ing on the condition of the

surface. Particularly advis-

able for bare copper surfaces

with little oxidation is the

single cross.

Maximum accuracy is

achieved due to the high in-

formation content. Rectan-

gle, square and circle are less

“informative” but save space

and can even be used when

oxidation is at an advanced

stage. Advisable for tinned

structures are circle or square

because in this case the ratio

of the fiducial dimensions to

the presolder thickness is

particularly favorable.

Fiducial criteria

Locate 2 fiducials

Locate 3 fiducials

X-/Y-position, rotation angle, mean PCB distortion

in addition: shear, distortion in X- and Y-direction separately

Fiducial shapes Synthetic fiducials: circle, cross, square, rectangle, rhombus,

circular, square, and rectangular contours, double cross

any pattern

Fiducial surface:

copper

tin

without oxidation and solder resist

Warp ≤ 1/10 of structure width, both with good contrast to

environment

Dimensions of synthetic fiducials

min. X/Y size for circle and rectangle: 0.25 mm

min. X/Y size for annulus and rectangle: 0.3 mm

min. X/Y size for cross: 0.3 mm

min. X/Y size for double-cross: 0.5 mm

min. X/Y size for lozenge: 0.35 mm

min. frame width for annulus and rectangle: 0.1 mm

min. bar width / bar distance for cross, double-cross: 0.1 mm

max. X/Y size for fiducial shapes: 3 mm

max. bar width for cross / double-cross: 1.5 mm

min. tolerances, general: 2% of nominal dimension

max. tolerances, general: 20% of nominal dimension

Dimensions of patterns

min. size

max. size

0.5 mm

3 mm

Fiducial environment Clearance around reference fiducial not necessary if there is

no similar fiducial structure in the search area

Vision Sensor Technology

Bad Board Recognition

Position Recognition for Feeder Modules

Description

In the cluster technology

each subpanel is assigned an

ink spot. If this is present dur-

ing the measurement via the

PCB vision module, the corre-

sponding subpanel is popu-

lated.

It is also possible to accom-

plish the population of the

subpanel when the ink spot is

missing. With this function it

is possible to eliminate costs

due to unnecessary popula-

tion of faulty subpanels.

Global Ink Spot

Each GOOD/SCRAP scan takes

some time, and the time re-

quired is even greater if there

are a large number of sub-

panels on a PCB. Using the

global ink spot can result in a

significant reduction of these

secondary times.

The PCB vision module

searches at positions taught

before for the defined fidu-

cial. In case of recognition

there is no following evalua-

tion of subpanels. The sys-

tem allows the operator to

choose also the reverse inter-

pretation.

Recognition of the position

of the feeder modules

The pick-up position of the

components can be deter-

mined precisely with the aid

of the position recognition

for the feeder. The offset in

position relative to the stored

ideal position is determined

on the basis of fiducials on

the feeder modules using the

PCB vision module.

This provides very high pick-

up reliability even for the

very first component, which

is particularly important for

small components.

Ink Spot Criteria

Methods • Synthetic fiducial recognition method

• Mean grayscale value

• Histogram method

• Template matching

Shapes and sizes of fiducials/structures for

synthetic fiducials

other methods

for dimensions of synthetic fiducials, see page 22

min. 0.3 mm, max. 5 mm

Masking material good coverage

Recognition time depends on the method: 20 ms - 0.2s