Visual engineering MKX Manuel d'utilisateur télécharger pdf (Page 5)

VISION

iVu Sensors PresencePLUS SENSORS LENSES LIGHTING

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A vision sensor captures and then analyzes an electronic image. The quality of

the inspections depends on the image’s contrast. Dedicated lighting can

guarantee constant, consistent light conditions that can be manipulated to create

a high-contrast image.

Here are some factors to consider when choosing lighting:

1. Lighting geometry

2. Techniques

3. Optical properties of the part

Lighting Geometry

The geometry of propagation refers to how light energy leaves the source.

Light can come from a point, diffuse or collimated source. When you understand

how to manipulate lighting geometry, you can:

• Maximize contrast

• Eliminate glare

• Eliminate hot spots

• Minimize unimportant

features

Vision Lighting

Lighting Techniques

Lighting techniques refer to how the light source is mounted in relation to the

target object and the sensor.

Dark-Field: Illuminate objects

with indirect light.

• Casts shadows

• Highlights height changes

• Textured surfaces are bright

Bright-Field: Illuminate objects

with direct light.

• Detect color change

• Smooth surfaces are bright

Backlight: Transmit light from

behind the object.

• Highlights outlines and profiles

• Highest contrast

Dark-Field:

illuminates object with indirect light.

Dark Field Dark Field Bright Field Bright Field

Object

Bright-Field:

illuminates object with direct light.

Dark Field Dark Field Bright Field Bright Field

Object

Backlight:

transmits light from behind the object.

Vision Sensor

Vision Sensor

Dark Field Dark Field Bright Field Bright Field

Object

Dark-Field:

illuminates object with indirect light.

Dark Field Dark Field Bright Field Bright Field

Object

Bright-Field:

illuminates object with direct light.

Dark Field Dark Field Bright Field Bright Field

Object

Backlight:

transmits light from behind the object.

Vision Sensor

Vision Sensor

Dark Field Dark Field Bright Field Bright Field

Object

Dark-Field:

illuminates object with indirect light.

Dark Field Dark Field Bright Field Bright Field

Object

Bright-Field:

illuminates object with direct light.

Dark Field Dark Field Bright Field Bright Field

Object

Backlight:

transmits light from behind the object.

Vision Sensor

Vision Sensor

Dark Field Dark Field Bright Field Bright Field

Object

Collimated

Source

Structured

Light

Diffuse

Source

Optical Properties of a Target

Optical properties of a part can be used in conjunction with lighting to highlight features.

Backlight Directional Ring Low-Angle Diffused On-Axis Structured

The main goal of lighting in

a vision application is to

create contrast between the

features and the background.

Optical Example

Properties Parts

Shape

Notches

Stampings

Embossing

Highlights

outlines and

profiles

Casts shadows

to highlight

height changes

—

Height changes

are bright

Flat

surfaces

are dark

Lowers

contrast

between shapes

Flat surfaces

are bright

Height changes

are dark

Highlights

changes in

height of part

Surface

Texture

Polished metal

Sandpaper

—

Textured surfaces

are bright

Smooth surfaces

are dark

—

Diffuse surfaces

are brighter

than reflective

Lowers contrast

between reflective

and textured

surfaces

Reflective surface

are brighter

than diffuse

—

Color

Wires

Printing

Plastic

UV Coatings

—

Based on

target color

Based

on

target color

—

Based on

target color

Based on

target color

—

Translucency

Drilled hole

Plastics

Solid parts block

light, clear parts

transmit light

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Courtesy of Steven Engineering, Inc.-230 Ryan Way, South San Francisco, CA 94080-6370-Main Office: (650) 588-9200-Outside Local Area: (800) 258-9200-www.stevenengineering.com

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