(IR) Machine Vision Lighting
use infrared imaging?
Infrared (IR) machine
vision lighting enables vision systems to properly
recognize an object and its condition under difficult lighting conditions; for
example, reflective surfaces that produce high levels of visible-spectrum
noise, excessive or extremely low levels of illumination or target areas with
variable light intensities. IR has a longer wavelength than visible light so can transmit further
into certain materials such as glass, semiconductor, paper, cloth and plastic.
As a result, certain defects or flaws can be detected with IR which cannot be
seen with visible light.
Machine Vision System Considerations
When building an IR vision
system, the correct combination of camera, lighting and software components must
be considered. For cameras, the speed of
measurement, level of sensitivity and price are important factors when deciding
on the optimum system configuration. The choice of illumination directly
affects the choice of camera since different camera sensors have different
optimum wavelength sensitivities.
In machine vision, most
of the IR applications are located in the near infrared range, which comprises
the spectral range from 780 to 3000 nm. NIR cameras for machine
vision are primarily based on Silicon (Si) or Indium-Gallium-Arsenide (InGaAs) based
sensors where Si is sensitive to light in the range of
400 to 1000 nm and InGaAs cameras are sensitive to light in the
range of 900 to 1700 nm.
Infrared Machine Vision Lighting
Designing any machine
vision system is as much about managing trade-offs as it is about optimizing
the systems performance at an acceptable cost.
The material under
inspection determines the range of wavelengths that can be utilized as
different materials absorb different wavelengths more easily. It is important
to choose your wavelength correctly as even wavelengths a few nanometers apart
can have wide variations in price and optical efficiency.
Once the wavelength or
wavelengths have been selected, the overall scene to be illuminated needs to be
examined to ensure the illumination solution captures the relevant information
in the camera sensor. It is important to consider the size of the illumination
area and understand what shadows and reflections will be present during the
systems operation. The beam profile, the intensity, the working distance and the
positioning of the illumination module are critical to producing the optimum
illumination profile. Careful design of the LED layout, lenses and reflectors
maximize the modules performance. All of these factors need to be considered
while taking into account that there can be strict constraints on the modules form
factor when integrating IR illumination modules into OEM systems.
IR illuminators operating at high intensities or
located in constrained or enclosed spaces benefit for well-designed
heat-sinking. Good thermal design will take the environment, IR LED packing
density, specified run time, current drive rates, strobe flash, and correct
heat-sink material into consideration to develop the proper solution ensuring
the efficacy of the LED illuminator and longevity of the LED chips.
ProPhotonix specialize in developing
custom IR LED solutions to maximize our customers’ system performances by
focusing on wavelength precision, uniformity control, power management and