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7 Vision Systems SIPLACE 80S /F/G User’s Manual 7.2 PCB Vision S ystem Edition 07/97 from Software Version S R.010.xx 7 - 14 Line engine er and the di splay LE D's for – the CPU – the visio n process or – the came r…

SIPLACE 80S/F/G User’s Manual 7 Vision Systems

Edition 07/97 from Software Version SR.010.xx 7.2 PCB Vision System

Line engineer 7 - 13

7.2 PCB Vision System

The PCB vision system senses the precise position of the board by scanning the fiducials and determines the

offset in x and y directions, the rotation angle relative to the direction of PCB transport and the shear of the

PCB. Even reject fiducials (ink dots) are registered by the PCB vision system and evaluated.

7.2.1 Description of the System

The PCB vision system for PCB position recognition consists of

●

the optical system for PCB position recognition.

Each revolver head is equipped with its own PCB position recognition system (see Fig. 7.1.2).

On auto-

matic glue application machines, the PCB camera system is located beneath the gantry

(see Fig. 7.1.8,

page 7 - 10).

PLEASE NOTE:

PCB position recognition is only carried out with gantry 1.

●

the vision evaluation unit.

For each gantry one evaluation unit for the position recognition of PCBs and components is installed in the

control unit (see Figures 7.1.3, 7.1.6 and 7.1.9). The adhesive application head is only equipped with one

system for PCB position recognition.

A CCD camera (Sony XC77 camera) with integrated imaging and lighting lens constitutes the optical PCB

position recognition system. The field of view of the PCB module equals 5.7 mm x 5.7 mm. Within the dimen-

sions of the visual fields a search area can be freely programmed with respect to position and size. The imag-

ing lens is a special measuring lens which provides the most extensive compensation for measurement errors

due to warping of PCB's. The lighting is only switched on when fiducials are being scanned.

The vision evaluation unit (MVS) is a single-board system in accordance with the VME standard. The hard-

ware consists of:

●

the MVS100 motherboard with vision processor and interface connections

The rear side of the board accommodates the

–

plug connections for the VME bus and

–

the very-high-speed communications unit (HS

The front side of the board accommodates the connectors for

–

the screen

–

up to 4 camera inputs

–

two serial interfaces (RS232 or RS422)

Placement System PCB camera MVS evaluation unit

80S (2 gantries) 2 2

80F (1 gantry) 1 1

G (1 gantry) 1 1

7 Vision Systems SIPLACE 80S/F/G User’s Manual

7.2 PCB Vision System Edition 07/97 from Software Version SR.010.xx

7 - 14 Line engineer

and the display LED's for

–

the CPU

–

the vision processor

–

the camera input

–

the screen display.

The switches for “RESET” and “ABORT” are located below the display LED's

●

the MVS500 camera interface (piggyback board) for up to four CCD cameras.

7.2.2 Technical Data

Camera type: SONY XC77

Number of pixels: camera 768 (H) x 494 (V)

image 640 (H) x 484 (V)

Field of view: 5.7mm x 5.7 mm

Lighting method: incident-light illumination (is activated during measurement)

Image processing: correlation principle, grey-scale system

Processor cycle time: < 200 msec

Screen: RGB monitor (VGA mode) 640 x 484 pixels of the stations

computer

Fiducials: library for up to 255 fiducial definitions

7.2.3 Description of Function

Before placement position, rotation angle and shear of the board are determined on the basis of the positions

of the fiducials by the PCB vision system. Deviations from the setpoint values are then included in the calcula-

tion of the placement positions of the components as corrections.

At least 2 fiducials must be marked on a board so that the system can recognize deviations in the PCB posi-

tion and in the PCB rotation angle. Where 3 fiducials are marked, you will be additionally provided with infor-

mation on compression and deformations of the board and of the board layout.

7.2.4 Functional Sequence

Before a fiducial can be used for PCB recognition, it must first have been “taught”, i.e. the fiducial structure

parameters must be stored in the PCB vision system for the pattern.

●

The fiducial structure is taught using the PCB vision camera fitted to the placement head and the vision

program.

The vision evaluation unit determines the significant fiducial structure parameters using methods of digital

image processing.

●

Measurement takes place in two steps:

–

2D pattern search procedure (2-dimensional procedure) in the rough grid and provisional determina-

SIPLACE 80S/F/G User’s Manual 7 Vision Systems

Edition 07/97 from Software Version SR.010.xx 7.2 PCB Vision System

Line engineer 7 - 15

tion of the fiducial coordinates

–

1D pattern search procedure (1-dimensional procedure) for precise determination of the position of

the fiducials.

With the 2D pattern search procedure the template window is divided into in moxel areas. Moxels (

saic pi

s) are pixel fields with, for example, 16 x 16, 8 x 8 pixels etc. The lower the number of pixels, the higher the

resolution and the lower the search speed.

Fig. 7.2.1 Explanation of camera field of view, search area and template window

The template window is moved over the search area in moxel steps. The grey-scale values of each individual

moxel of the reference pattern are calculated. This reduced data structure contains enough information on the

rough structure and position of the reference pattern.

NOTE

The search window should be selected as small as possible in order to achieve a high search speed, but

should still be large enough to ensure clear reidentification of the fiducial.

The 1D pattern search procedure is used for the exact determination of the pattern and position of the fiducial.

The fiducial image is analyzed by column and row and the grey-scale values within each individual column

and row added up. The next Figure shows this procedure using a double cross.

Search area for the

camera

≤

field of view

(The fiducial is

searched for within

this area)

Reference pattern

Moxel = pixel field

e.g. 16 x 16 pixels

Field of view of the camera

Fiducial to be found

Template window

(It contains the reference fiducial)