QMT Features: October 2016
Remote inspection in 3D

Liam Hanna* of Olympus looks at how 3D stereo measurement is transforming the way videoscopes reveal crucial data

Remote visual inspection (RVI) is a valuable tool when inspecting complex equipment, reducing cost and time, avoiding the need to disassemble critical components such as gas turbines and piping infrastructure. Since videoscopes face the challenge of fitting complex optical and digital imaging equipment into the compact tip of the scope, inspection and measurement capabilities have traditionally been limited. However, in light of technological advances in miniaturisation, digital imaging quality and data processing power, the next generation of videoscope has progressed RVI to a new level.

Equipped with sophisticated engineering and 3D stereo measurement capabilities, the latest videoscopes such as the Olympus IPLEX NX vastly enhance Probability of Detection (PoD) and flaw characterisation for extra confidence in decision-making. This article explores breakthrough inspection possibilities through direct real-world examples - illustrating how accurate measurements are guaranteed in conditions where standard videoscopes fail - and discuss the innovative technologies underpinning these capabilities.

Advanced 3D stereo measurement
Our eyes use 3D stereo measurement to estimate sizes or distances. Industrial videoscopes work in a similar way, but instead use a measurement tip to focus and detect the image. When a point on an object is detected with a single measurement it is not possible to obtain accurate distance measurements. 3D stereo measurement can address this issue by measuring an object from two slightly different positions and determine the distance by parallax and triangulation (Figure 1).

Optimising the process of stereo measurement on a small diameter tip, videoscopes use a two-lens setup to project the object onto a single CCD camera from two different angles. This setup makes it possible to obtain detailed information about the distance between the object and the measurement tip of the videoscope.
Various improvements in technology including image acquisition, processing and optics have enabled advances in 3D measurement, giving rise to the so-called ‘super wide field’ 3D stereo measurement. These improvements include better optics, laser diode illumination and improved CCD imaging sensors (cameras).

Increasing PoD, the latest optics and a more sensitive CCD have given rise to significant increases in both the Field of View (FoV) and the Depth of Field (DoF); increasing FoV by 50%, and the DoF even further, 70% compared to conventional videoscopes, meaning that defects that are 4 x larger than conventional videoscopes can be measured.

Gaining access to those hard-to-reach areas, these improvements have also resulted in a considerable expansion of the range of ‘tip-to-target’ distances over which measurements can be performed. Where, in standard models the tip-to-target distance range is limited to 5-30 mm, this range has more than doubled in the latest videoscopes. Combined with advanced scope tip articulation this enables an unprecedented level of detail when measuring and imaging areas that are difficult to reach.

These features, as well as increased resolution twinned with enhanced laser illumination systems, have evolved the inspection workflow, making it easier than ever to inspect, check and measure in just three simple steps (callout box).
Increasing PoD where standard videoscopes fail.

As discussed, technological advances in RVI technology have resulted in several important benefits for the end-user, especially with respect to limitations associated with day-to-day use of RVI technology. The series of case studies below highlight the real-world value that the latest videoscope benefits afford when measuring, for example, thin features, reflective surfaces, dark compartments and objects under acute angles.

Measuring thin features

Objects with small or narrow features are very common targets for videoscope inspections and measurements. Many of these targets may have surface areas that are too narrow perform measurements on. Using the latest super wide field 3D stereo measurement enables the distal end of a component to be measured with greater accuracy (figure 2).

Reflective surfaces
Many of the targets that are measured with RVI have surfaces which are highly reflective; these include metals, glasses and oily surfaces. Particularly in the aerospace and automotive industry, it is highly advantageous to be able to generate accurate measurements under these conditions, yet the bright reflections of these surfaces will often render the rest of the image too dark to measure (figure 3). Using cutting-edge image processing technology on the latest RVI technology, images of reflective surfaces can be modified to reduce this effect automatically and add more contrast to darker regions.

Bringing dark objects to light

Another RVI innovation is an improved method for illuminating dark compartments and high-absorbance materials. Showing considerable improvement over conventional LED-based systems, laser diode illumination has the capacity to deliver light at a higher intensity resulting in brighter illumination and allowing measurements at a wider range of distances.

Angled surfaces

The latest image processing techniques can also act as a valuable tool in the analysis of angled surfaces. Often, surfaces that are hard to reach can only be illuminated from one angle causing non-uniform illumination. Using brightness control this problem can be corrected in real-time allowing measurements to be carried out over much greater distances. This is an important feature, for example when inspecting the inside surfaces of pipelines.

Measuring hard-to-reach areas
To achieve the best possible results with new RVI devices, a target distance of around 40 mm from the target object is recommended, compared to 20 mm required with standard videoscopes. In order to test measurement accuracy of the IPLEX NX against an extreme target distance and under adverse conditions, a measurement was conducted against a known distance of a calibrated rule of 100 mm (+/- 0.5 mm) length, from a target distance greater than 200 mm (192.8–204.8 mm). The surface of the rule was highly reflective, in order to place the system under the most adverse conditions possible and to understand the accuracy achievable in the worst case scenario. While a standard videoscope was unable to achieve any measurement data, this videoscope was able to take a measurement with 99.79% accuracy.

Advanced, Super Wide Field 3D stereo measurement is an invaluable tool for RVI as it helps to convert images into reliable, consistent, tangible data. The precision with which these measurements can be obtained, however, relies on using the very best optics and image processing software available. All these elements have been brought together in the latest generation of industrial videoscopes for unprecedented quality and precision.
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