Surface Inspection with Photometry-Based Imaging Systems

A new class of automated visual inspection technology, Advanced Vision, combines the sensitivity of true human vision with the automation advantages of traditional machine vision to identify subtle cosmetic defects and ensure consistent product quality.

Customers expect flawless electronic devices right out of the box. Dented, scratched, and otherwise imperfect products can damage a brand’s future business and reputation.

To ensure consistent visual quality in the cosmetic appearance of delivered products, human quality inspectors use their immediate qualitative judgment and acute visual perception to identify imperfections, regardless of how or where they may occur.

Yet, quicker production rates make it hard for humans to consistently identify subtle defects while keeping up with throughput demands. Automated (machine-based) inspection systems inspect with better consistency and speed, but traditional machine vision systems cannot match the visual sensitivity and adaptability of humans.

Photometry-based Vision Systems

Photometry-based imagers are designed to identify subtle light variations. These systems are correlated to human visual sensitivity and are traditionally used for measuring uniformity and brightness across large spatial areas such as an illuminated display.

Radiant’s Advanced Vision method utilizes photometry-based imaging to combine the precision and adaptability of human vision with the consistency and speed of machine automation. Their capabilities surpass those of traditional machine vision cameras for inspecting particles and imperfections in glass or cosmetic defects on surfaces.

Photometric imaging systems quickly detect anomalous features, like the human eye. Then software grades these defects based on their scope, location, and severity so manufacturers can make a choice to rework, ship, discard, or repair, a device.

Luminance variations are detected across a device surface using Radiant’s ProMetric Y29 (29 megapixel) Imaging Photometer (top), indicating surface defects like scratches or dents. Only a limited set of these luminance variations are detected by a 71-megapixel CMOS imager (bottom), missing one peak variation at around 0.08 meters that indicates a cosmetic scratch, which was detected by the ProMetric camera.

Luminance variations are detected across a device surface using Radiant’s ProMetric Y29 (29 megapixel) Imaging Photometer (top), indicating surface defects like scratches or dents. Only a limited set of these luminance variations are detected by a 71-megapixel CMOS imager (bottom), missing one peak variation at around 0.08 meters that indicates a cosmetic scratch, which was detected by the ProMetric camera.

Scientific Imaging

Radiant’s visual inspection systems pair imaging technology and specialized optics with advanced algorithms to identify and characterize cosmetic defects. Their imaging systems have scientific-grade CCDs with dynamic range, extremely high resolution, and signal-to-noise ratio for repeatable and precise measurements.

By testing each CCD’s specifications and applying built-in sensor cooling, image noise is carefully decreased, allowing their CCD imaging systems to identify more defects and surface variations than even the highest megapixel CMOS cameras.

Sophisticated Software

In order to locate and characterize randomly occurring cosmetic defects on device surfaces, including unknown defects in unpredictable locations, Radiant solutions include sophisticated software algorithms.

Radiant solutions systems carry out uniformity checks to detect subtle dents, hairline scratches, and smudges across device surfaces by capturing a full spatial image of a device.

This photometry-based inspection method combines camera software and systems to “perceive” surface cosmetic defects in the way that humans do, first by capturing images with dynamic range and resolution that match human vision, and then using specialized algorithms to match human perception.

Just as humans use their judgment to establish a reasonable margin of error, Radiant’s Advanced Vision systems can classify the severity of each defect against acceptable tolerances and establish pass/fail.

Scratches on the back of a laptop are identified and qualified based on their severity. The values shown in this analysis image provide contrast ratios relative to a background level.

Scratches on the back of a laptop are identified and qualified based on their severity. The values shown in this analysis image provide contrast ratios relative to a background level.

Data Capture & Analysis

Unlike human inspectors, Radiant software applies numeric values to each defect to decide severity, quantifying defects by frequency, shape, location, size, and occurrence rate, and building trend analysis data to permit the user to improve product quality, fine-tune processes, and optimize production efficiency.

Inspecting the front and back surfaces of a tablet.

Inspecting the front and back surfaces of a tablet.

Flexibility

Built on Radiant’s automated visual inspection software, their Advanced Vision systems can simultaneously perform inspections for assembly verification, fit & finish analysis, part orientation, and text/label legibility, stopping the requirement for a separate machine vision system to undertake these inspections on the line.

The length and width of a dent can be measured against  defined thresholds to determine if the product passes or fails.

The length and width of a dent can be measured against  defined thresholds to determine if the product passes or fails.

Capability

Photometry-based vision systems are ideal for cosmetic inspection of device surfaces (buttons, marks, case, bezel, etc.). These systems can detect defects on glass like smudges, in addition to defective features in device housing, which use Radiant’s extensive light measurement algorithms for identifying “mura” in illuminated displays.

Eliminating Particle Defects on Surfaces

Radiant systems are also able to detect unwanted particles on glass, surfaces, and transparent layers due to their high-dynamic-range (up to 61 dB depending on sensor option) CCD imaging, and extremely high-resolution (to 43 megapixels).

Dynamic range heightens the amount of grayscale values in each image, to ensure that subtle contrast variations are identifiable to examine fine details. So they can be identified and removed before shipping, the specifications of Radiant cameras ensure that pixel-sized particles are clearly discernible from image noise.

Radiant automated visual inspection software detects  particles on this metallic surface, which can cause unwanted variations in surface finish.

Radiant automated visual inspection software detects  particles on this metallic surface, which can cause unwanted variations in surface finish.

The Power of Advanced Vision

Utilized for cosmetic surface inspection, Advanced Vision systems supply all the advantages of automated inspection, including quantifiable results and objective analysis, while gathering the data required for error tracking to optimize production operations.

Radiant software supplies an extensive set of machine vision inspection tools for production-level monitoring and pass/fail test sequencing to enable manufacturers to automate any visual quality inspection process.

Radiant’s photometry-based systems can be utilized to inspect components with imperceptibly precise tolerances, such as glass & transparent layers (particle detection, air bubbles), keyboards (measuring gaps between characters, keys, etc.), and more. They can identify defects that may be missed by human inspectors.

Advanced Vision inspection addresses assembly verification and all aspects of appearance, fit, and finish.

This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.

For more information on this source, please visit Radiant Vision Systems.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Radiant Vision Systems. (2019, October 29). Surface Inspection with Photometry-Based Imaging Systems. AZoOptics. Retrieved on November 12, 2019 from https://www.azooptics.com/Article.aspx?ArticleID=1669.

  • MLA

    Radiant Vision Systems. "Surface Inspection with Photometry-Based Imaging Systems". AZoOptics. 12 November 2019. <https://www.azooptics.com/Article.aspx?ArticleID=1669>.

  • Chicago

    Radiant Vision Systems. "Surface Inspection with Photometry-Based Imaging Systems". AZoOptics. https://www.azooptics.com/Article.aspx?ArticleID=1669. (accessed November 12, 2019).

  • Harvard

    Radiant Vision Systems. 2019. Surface Inspection with Photometry-Based Imaging Systems. AZoOptics, viewed 12 November 2019, https://www.azooptics.com/Article.aspx?ArticleID=1669.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit