Versatile LEDs Drive Machine Vision in Automated Manufacture | DigiKey
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`Versatile LEDs Drive Machine Vision in Automated Manufacture
`By European Editors
`Contributed By Publitek Marketing Communications
`2012-01-03
`
`About this author
`European Editors
`
`Article provided by Publitek European
`Editors
`
`About this publisher
`
`Publitek European Editors are expert
`technical writers that produce articles
`for publication by electronic
`component manufacturers and
`distributors, related technology
`businesses, and both trade and
`business media. The team is a
`division of Publitek Marketing
`Communications, the world’s leading
`B2B technical content marketing
`and technology PR agency for the
`electronics industry.
`
`Figure 1: Machine vision, which increasingly takes advantage of illumination by LED light sources, often replaces
`human inspection in automated production lines (Courtesy of Schott).
`
`In machine-vision systems, the typical low power requirements and long lifetime of LED-based lighting have
`made solid state lighting (SSL) the preferred choice for illuminating automated manufacturing systems.
`
`A variety of LED-based ring-lights, dome lights, backlights, and spotlights based on LED technology are
`available. Due to a combination of the reliability of this technology and the phasing out of traditional incandescent
`or fluorescent light sources, the marketplace and deployment of LED systems continues to expand. Lighting
`vendors are building on these developments to offer different configurations of LED products to meet the needs
`of specialized machine-vision applications.
`
`Historically, fluorescent and quartz halogen lighting sources have been used most commonly. In recent years,
`LED technology has improved in stability, intensity, and cost-effectiveness. Although it is still not as cost-effective
`for large area lighting deployment, particularly compared with fluorescent sources, LED lighting may be more
`appropriate if application flexibility, output stability, and longevity are important parameters .
`[1]
`
`Technical advantages
`
`LEDs are highly reliable, long-lasting illuminants with low maintenance requirements. Also, as DC voltage-
`powered components, they do not exhibit 100 Hz flickering – unwanted beats or overlapping when using CCD
`cameras. LEDs can be continuously dimmed down to zero percent light. Their instant start property facilitates
`strobe operation as well as externally triggered pulse operation.
`
`LEDs’ relative insensitivity to motion and vibration and their low weight make it possible to use LEDs in moving
`machine vision applications (for example in robotic systems). Because of their small size, LEDs can be used to
`produce special illumination components that provide optimum contrasting for specimens in machine vision.
`
`Because of their compact modular design, it is easy to develop LED components, for example ring-lights, which
`can be controlled in segments. In this way, a significant contrast enhancement (of images) is achieved compared
`with full circle illumination. When steering several illumination components via a common control unit, it is easy to
`generate mixed light and to quickly switch over between different types of illumination. Modern “intelligent”
`control units make it possible to completely control the LED illumination of subjects by PC, which facilitates exact
`specification of illumination settings
`[2]
`
`Machine vision needs
`
`LED-based lighting is used in many industrial machine-vision inspection systems to help determine / confirm the
`shape of parts in manufacture – by defining edge geometry, or enabling the size and position of drilled holes to
`be imaged and verified. Manufacturers often want to change the product they are inspecting on a given
`production line, so the LED lighting types, power, wavelength and associated optics and cameras need to be
`flexible enough or interchangeable to allow adjustment.
`
`http://www.digikey.ca/en/articles/techzone/2012/jan/versatile-leds-drive-machine-vision-in...
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`10/7/2015
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`Magna 2037
`TRW v. Magna
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`Versatile LEDs Drive Machine Vision in Automated Manufacture | DigiKey
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`Page 2 of 5
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`Figure 2: Diverse effects of various LED-based lighting techniques on a ball bearing (Photo courtesy of
`[3]
`Microscan).
`
`A key consideration when choosing any type of lighting is the configuration of the light source and its spectral
`properties. Besides considering the uses of different cluster designs – whether backlights, ring lights, and other
`designs of illumination units – the types of the fitted LEDs must also be chosen carefully. Variables such as
`output wavelength, power and geometry must suit the application. The choice will depend on the color and/or
`reflectance of the parts under inspection.
`
`Figure 3: Cree’s XLamp CXA2011 LED array is suited to Machine vision (Courtesy of Cree).
`
`Advanced Illumination (Rochester, VT, US) is a machine vision manufacturer of LED lighting products. John
`Merva, Vice President of Sales & Marketing, said, “We make lighting units of different sizes and shapes,
`wavelengths, and power for applications in just about any manufacturing operation that is automated.
`
`Traditional lighting sources, such as incandescent or fluorescent, had problems of relatively short lifetime and
`inconsistent output – especially near the end of life – wavelengths and brightness tend to change, which is why
`LEDs are much more reliable and preferred today. The LED manufacturers we tend to favor are the main three:
`Nichia , Cree and Phillips-Lumileds , among others.”
`[4]
`[5]
`[6]
`
`Figure 4: Light source relative intensity vs. spectral content. Bar at bottom denotes approximate human visible
`wavelength range (Source: Advanced Illumination ).
`[1]
`
`It might appear that the ever-growing selection of LED light sources would make finding the ideal sources easier
`but the increasing diversity actually means that systems developers need to do more R&D. Considering new
`sorts of SSL sources, such as OLEDs, Merva said he considers these alternative sources but added, “the
`changes that happen in this industry sector tend to happen rather slowly.”
`
`http://www.digikey.ca/en/articles/techzone/2012/jan/versatile-leds-drive-machine-vision-in...
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`Versatile LEDs Drive Machine Vision in Automated Manufacture | DigiKey
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`Commenting on trends in the use of LEDs for machine vision systems, Merva said, “The types of the LEDs we
`normally use are split between the different colors of visible light and the higher power white LED sources. In the
`early days, machine vision used red LEDs because of their relative high power, low cost and wide availability but
`more recently red has been superseded by white, in conjunction with full color cameras.”
`
`Machine vision and its reliance on solid-state lighting will continue to grow. We are seeing the number of camera
`deployment points growing across industry and elsewhere, especially considering that a “smart” camera can now
`be purchased for under USD 2,000. Historically, the vision problem needed to be significant to justify the cost of
`deploying cameras but nowadays it can be relatively minor and the savings will still justify the cost of the LED-
`based vision system. Furthermore there is a multitude of more complex manufacturing techniques going on, so
`there is room for growth, Merva believes, “possibly by a factor of ten greater than today’s penetration because
`these technologies are solving customers’ problems at the right price.”
`
`Back and edge lighting
`
`To achieve ideal illumination, many systems builders use an array of surface-mounted LEDs across the backlight
`with a diffuser positioned to produce even lighting. This results in a high-brightness backlight with a relatively
`thick display. To reduce this thickness – space is always at a premium in the manufacturing environment – some
`manufacturers also offer edge-lit backlights in which the LEDs are placed around the outside of the display and
`light transferred across the face of the display by a diffusion plate.
`
`Moritex USA, based in San Jose, CA, offers both types of backlights. Its MDBL series provides a higher
`luminance than its edge-type MDBC series, whereas the MDBC series’ thinner design is more useful in
`applications with space constraints. Phlox, Aix en Provence, France, and Lumitex, Strongsville, Ohio, US, offer
`different variations of this technique in their range of machine-vision lights. Phlox uses a PMMA
`(polymethylmethacrylate) pipe lit by a linear LED source in its range of backlights; Lumitex uses an optical fiber
`mounted on a back reflector to create lighting panels as thin as 0.33 mm.
`
`Christophe Blanc, Phlox director (and patent holder) said, “At Phlox, we only make a small part of the machine
`vision lighting system; we make backlights for which we use LEDs in conjunction with light pipe technology. We
`use PMMA and we manufacture a groove on top of the acrylic plate. The groove extracts the light, so we
`effectively inject light from the side of the plate.”
`
`For its visible spectra applications Phlox deploys only Nichia LEDs . Nichia was the original manufacturer of
`[4]
`white LEDs (invented by Shuji Nakamura, who nowadays works for Cree ). The company uses only Nichia
`[5]
`white/blue gallium nitride LEDs except for infrared applications. For its infrared machine vision applications,
`Phlox previously used Osram-OS LEDs but more recently the company has been working more with infrared
`[7]
`LEDs from the Taiwanese supplier Lite-On .
`[8]
`
`As well as developing novel configurations such as flat dome lights, LED lighting manufacturers typically offer a
`range of different wavelengths for different applications. Aside from the more traditional product offerings using
`white, red, green, and blue LEDs, UV and IR lights are becoming increasingly popular to perform more complex
`vision inspection applications. These include systems where materials to be inspected may exhibit fluorescence
`or where operating personnel must be shielded from bright LED illumination. In other cases, illumination products
`that combine LEDs with multiple wavelengths are being used to reduce the number of inspection stations
`required to inspect multiple facets of complex parts.
`
`Market conditions
`
`The LED-based illumination systems that Banner Engineering (Minneapolis, MN, US) supplies for automated
`manufacture range from ring lights to back lights, spot lights to linear array lights. Those are the vision-specific
`light designs.
`
`http://www.digikey.ca/en/articles/techzone/2012/jan/versatile-leds-drive-machine-vision-in...
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`10/7/2015
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`Versatile LEDs Drive Machine Vision in Automated Manufacture | DigiKey
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`Figure 5: Banner Engineering’s High Intensity Area Lights are available in sealed IP69K versions so are suited to
`machine vision applications in food and beverage manufacture.
`
`Chuck Dolezelack, Engineering Manager, said, “Because we offer sealed IP69K versions of many of our lights,
`our systems have presence in wash down environments, such as those found in the food and beverage
`industries, as well as pharmaceutical and medical and material handling industries. Specific applications range
`from illuminating small parts for sorting or matching functions, or casting a shadow for error-proofing purposes.”
`
`Dolezelack believes that the main problem remaining to be solved is energy efficiency and that the likely
`evolutionary path for these LED lighting systems is that they will become even more rugged and consume less
`power as the technology advances.
`
`“Today’s market conditions are such that as manufacturing goes, the LED lighting systems will follow,”
`Dolezelack said. “Right now, lighting and indication is [Banner’s] fastest growing product division because of its
`utility as well as its simplicity, and because manufacturing is strong for the moment.”
`
`Applications
`
`The machine vision department of Polytec, Waldbronn, Germany, supplies a wide range of LED illumination
`solutions for machine vision. The range is expanded by sister company Latab, Vällingby Sweden, giving a total of
`more than 3000 products. Polytec also offers many different controllers, subdivided into continuous mode and
`strobe mode.
`
`Hendrik Schumann, head of machine vision at Polytec, said, “In Germany, the automotive industry is for sure the
`most important user for machine vision applications. All vehicle manufacturers have to ensure 100% quality
`control of every part. But increasingly in the food or electronic industries and in general industry everywhere,
`machine vision systems based on LEDs are used to ensure product quality.”
`
`“LEDs’ power and optics are not themselves key components for successful illumination. The key is the perfect
`cooperation between LED, system mechanics and the quality of the current supply; LEDs are driven by current
`and not by voltage.”
`
`Figure 6: Osram-OS’s Ostar Observation infrared LED, model SFH4750 (Source: Osram-OS).
`
`For white lighting, Polytec deploys LEDs from Bright View and Osram-OS LEDs for red lighting. Latab’s
`[9]
`[7]
`machine vision illumination solutions typically operate at the following wavelengths: red 617 nm, IR 880 nm, blue
`465 nm, green 520 nm and UV 395 nm and 365 nm. Typical operating currents range between 30 mA and 3000
`mA in continuous mode and seven times higher in strobe mode.
`
`Considering the current market and likely evolutionary path for this area of technology, Schumann commented, “I
`expect that the brightness of LEDs will increase enormously in the future and consequently new markets will
`arise. Perhaps it will be also possible to use fewer LEDs than currently and that the illumination areas will be
`more focused but brighter. From a business perspective, machine vision-related LED sales are directly
`connected to the state of the mechanical engineering industry and therefore to the world economy.”
`
`Conclusion
`
`Any automated manufacturing process under inspection will undergo frequent changes in appearance to the
`vision system, whether it is the manufacturer’s intention to change product types or rate or whether it is due to
`variability of product quality.
`
`Consequently, if you want to guarantee a process 100% and maintain the product quality, a reliable observation
`method is critical. To ask human inspectors to do that is too much – especially when transportation rates are
`high, products are small or the variability is outside of the visible range. In short, humans do not have the
`patience and consistency to provide that level of reliability.
`
`Ultimately, advanced, non-contact, automated vision systems – which are increasingly based on LED illumination
`– are no longer optional extras for production lines; they are becoming an intrinsic part of the must-have fabric of
`the factory.
`
`http://www.digikey.ca/en/articles/techzone/2012/jan/versatile-leds-drive-machine-vision-in...
`
`10/7/2015
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`Versatile LEDs Drive Machine Vision in Automated Manufacture | DigiKey
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`References:
`
`1. http://advancedillumination.com/uploads/downloads/practicalguidemvlight.pdf
`2. http://www.us.schott.com/lightingimaging/english/download
`/visileds_extraordinary_illuminations_brighten_up_the_industry_1003_us.pdf
`3. http://files.microscan.com/_att/7e54b2b8-570c-4366-a740-5da5b0e5336c/
`lighting_tips_white_paper.pdf
`4. http://www.nichia.co.jp/en/about_nichia/index.html
`5. http://www.cree.com/
`6. http://www.philipslumileds.com/
`7. http://www.osram-os.com/osram_os/EN/
`8. http://www.us.liteon.com/
`9. http://www.bvled.com.tw/
`
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