COLOUR INSPECTION, INFRARED AND UV TIPS, SPECIAL FEATURES, REQUIREMENTS LARS FERMUM, CHIEF INSTRUCTOR, STEMMER IMAGING
THE PROPERTIES OF LIGHT Light is characterized by specifying the wavelength, amplitude and polarization. Electromagnetic radiation Wavelength λ Blue light has a shorter wavelength than red light (and more energy). The colour perceived by the human eye is the reflected light; all the other wavelengths have been absorbed. (Exception: self illuminating objects) X-RAY ULTRAVIOLETT VISIBLE Near-INFRARED Mid-INFRARED Far INFRARED 380-780 nm
WAVELENGTH RANGES UV Ultra Violet VIS Visible VNIR Very Near Infrared NIR Near Infrared MIR Mid Infrared LWIR Long Wave Infrared 380-780 nm 950 1700 nm 8000 15000 nm 190 380 nm 780 1000 nm 2000 5000 nm Silicon, direct detection (CCD & CMOS) HgCdTe Silicon, Fluorescence InGaAs Vanadiumoxid Amorphous Silicon InSb Liquid N 2 -cooled system Spectral detection using different wavelength ranges, not only in the VIS range with different semiconductor materials as detector
LIGHT GENERATION USING LEDS Fast cycle times, can be overdriven in strobe mode White, blue, green, red, amber UV: Typical 365, 385, 395, 405 nm IR: 850, 870, 940, 1050, 1200, 1300, 1450, 1550 nm etc. White LED Red LED Infrared LED (950nm)
CREATING CONTRAST
LIGHT VERSUS COLOUR Additive colour mixing Mixing coloured light Substractive colour mixing Colour absorption
ADDITIVE COLOUR MIXING Green LED Blue LED Red LED
LIGHT AND COLOURED OBJECTS Complementary light colour darkens a coloured object, same colour of light brightens the object. Red 630 nm Green 530 nm Blue 470 nm IR 850 nm
INSPECTING WITH UV Daylight UV radiation can excite fluorescent dyes that glow in the visible range and can thus be inspected. Examples: UV-active adhesives Security features UV-active inks Greases For better visualization, always combine with bandpass filter!
INSPECTING WITH UV Fluorescence security features with monochrome camera and bandpass filter Green fluorescent grease spots, inspection with colour camera
INSPECTING WITH IR Colour pigments absorb mainly in the visible wavelength spectrum. UV and IR radiation is barely absorbed, but reflected. Therefore, colours and colour prints appear bright. RGB camera, white illumination Monochrome camera, white illumination Monochrome camera, infrared illumination
SURFACE INSPECTION USING UV & IR Short-wave radiation tends to reflect more than long-wave radiation (stronger interaction with surface structure due to higher frequency; minimum penetration depth) UV radiation IR radiation UV radiation ideal for inspection of smooth surfaces Smooth surface Small features, dust and scratches are clearly visible ATTENTION: Consider LED photobiological safety classes (IEC 62471)
INSPECTING WITH IR Long-wave IR radiation is less scattering and penetrates materials better using a backlight. UV radiation: only reflection. Blue backlight, glue bottle Infrared backlight, glue bottle
SENSOR SENSITIVITY
SENSOR CHARACTERISTICS Sensitive across visible wavelength range Often highly sensitive to green light Also IR-sensitive, hardly UV-sensitive SONY IMX 174 CMOS, 2.4M 5.86ΜM SONY ICX 274 CCD, 2 MPIX 4,4ΜM Source: Allied Vision
INSPECTIONS WITH UV OR NIR Special CCD sensors with extended UV sensitivity down to 200 nm + fused silica cover or removed protective glass. InGaAs detectors for VNIR/ SWIR applications Jai CM 140 GE -UV Xenics Gobi 640 Source: JAI, Source JAI CM 140 UV Source: Xenics, Datasheet Gobi 640
SWIR CAMERAS WITH INGAAS DETECTOR (IR) InGaAs camera + (bandpass filter): Measurement of higher temperatures, different absorption and transmission behaviour of certain substances (e. g. water at 1450 nm) Hyperspectral Imaging: Identification of different organic substances, measurement of substance concentrations Colour camera Xenics Bobcat + bandpass filter 1450 nm Source: Perception Park
UV, VIS AND IR: OPTICAL CONSIDERATIONS
BEST OPTICAL RESULTS A large number of optical errors depend on wavelength as long as they are not extensively compensated with a complex lens design: Longitudinal chromatic aberration Lateral chromatic aberration Coma Astigmatism Spherical aberration
COLOUR CORRECTED LENSES Colour corrected lenses compensate longitudinal and lateral chromatic aberration effects Trick : Use of monochromatic light (for example blue or red LED!) Standard lens Light of different wavelengths generates chromatic longitudinal or lateral chromatic errors. Colour corrected lens Correct image without color fringing
ANTI-REFLECTION COATINGS Attention: Most lenses are not designed and coated for IR! Scattered light 0% 6% 12% 24% Blurred images Low-contrast images due to stray light Special IR lenses available (coatings, lens design) Mode of operation Anti-reflection coating
DIFFRACTION AT SLIT Light beam: the light spot is represented as diffraction disk ( airy disk ). These effects of blur are caused by diffraction at slit The ideal optical system is only diffraction limited, not limited by optical errors. Higher system resolution at shorter wavelengths! Light spots Aperture Figure 2: Diffraction with circular aperture Figure 3: Diffraction at double slit Source figure 1 +2: Wikipedia ( Beugung, Beugungsscheibchen) Diameter of airy disk d= 2*1.22 * κ*λ (κ=f-number, λ= wave length)
CONTROL AMBIENT LIGHT INFLUENCES
SUPPRESS EXTRANEOUS LIGHT Constant lighting situation, more robust applications Less pseudo errors, less work: saves time, money and hassle! Disturbing ambient light influences Bandpass filter blocks ambient light Source: Midopt
THANK YOU FOR YOUR ATTENTION Your contact Lars Fermum STEMMER IMAGING GmbH +49 89 80902-272 info@stemmer-imaging.de www.stemmer-imaging.de Copyright STEMMER IMAGING. All texts, images, graphs, tone, video and animation files as well as their arrangements are subject to copyright law and other laws for the protection of intellectual property. They may not be copied or changed for any commercial use or for the purpose of being passed on nor used on other websites. Some of the pages of the STEMMER IMAGING presentation also contain images that are subject to the copyright belonging to those persons who have made them available