February, 2016
www.us-tech.com
Choosing the Right Lighting for Machine Vision Applications
By John Lewis, Global Content Marketing Manager — Vision, Cognex Corporation M
achine vision systems create images by analyzing the reflected light from an object; not the object itself. A good image is
the result of proper focus and illumination. Images with poor contrast and uneven illumination require much more effort from the imaging com- puter, which increases processing time, and can lead to incorrect image analysis. For many years, machine vision has been a
critical tool in PCB assembly. Solder validation would be difficult or impossible to perform manu- ally, because of the density of components on the board. Machine vision not only inspects the connection, but also pro- vides feedback on defects in the event of solder cracking, inadequate reflow and other process characteristics. It also allows machines to place and ver- ify components, inspect PCBs for war - page, and perform a variety of other tasks.
Types of Lighting The wavelength of light used is
an important variable in the inspec- tion process. With illumination by light of a particular color, contrasting colors will be easier to differentiate, as they will appear dark in the image. This technique is effective when used to enhance the fiducial marks on a PCB, for example. Ultraviolet light will cause ink or
glue to fluoresce. Filters should be used on the camera if infrared or ultraviolet light are used to keep the light itself from being viewed rather than the fluorescence of the object. Collimated light, where the light rays are aligned so as to always be
An unveiling of innovative X-Ray inspection is coming
All Scienscope X-Ray inspection systems offer the best performance to price ratio in the industry
Back-lit light bulb. All the glare is avoided and internal features are easily seen.
parallel, is good for producing sharp images. Diffused light, which can be produced by taking collimated light and shining it through frosted glass, gives a softer and more even illumina- tion. This avoids causing glare or
There are five basic techniques for lighting parts under inspection: back lighting, direct lighting, structured
lighting, and on- or off-axis diffuse lighting.
shadows, though at the cost of reduc- ing the light’s intensity.
Back lighting creates a silhouette to accentuate the shape of a part and allow for its measurement, but totally obscures all surface detail. It creates the maximum amount of contrast by producing an image that is, for the most part, black on white. This tech- nique is suitable for dimensional measurements, but useless for surface inspection.
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Each machine is a complete package solution with no line item costs Advanced X-Ray tube technology High resolution flat panel detectors Camera tilt for oblique angle inspection up to 65° Rotation of test object up to 360°
Advanced automated and manual s/w tools for BGA, POP, CSP, and much more
Most user friendly GUI with simple point and click instructions, step-and-repeat, macros, etc
Reporting and traceability features Flexibility
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To see the latest innovation “behind the curtain”, or our popular X-Scope series (1800, 2000, 3000, and 6000), please make an appointment to see us at APEX, or send us your product and schedule a “live” online demo without leaving your factory.
Light bulb directly illuminated by a ring light. The ring light is reflected in the glass.
Direct lighting is a technique which is easy to set up and provides excellent contrast. Typically, light is set up to shine slightly off-center, at an angle to the object. This helps avoid shadows, which can be produced from direct lighting. In some situations, shadows may be desirable, to enhance contrast if low-contrast images are a problem. Direct lighting may also cause glare, depending on the surface of the part under inspection.
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Be sure to visit us at APEX 2016, booth 1038. In addition to the popular X-Scope systems,
Scienscope is proud to be introducing several new innovative products.
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