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Optical metrology - how it works in industry

Measurement News from Q-Tech

Optical metrology plays an important role in modern industrial manufacturing processes. Especially the high measuring speed characterizes these processes. 

How does optical metrology work in detail? Optical metrology is based on the use of light. Primarily, lengths, shapes and surfaces are measured. Compared to tactile measuring systems, optical processes can be carried out at a significantly higher speed. In addition, the measurement is non-contact, so sensitive components are not damaged. Optical 2D and 3D measuring systems can be used for the measurement.

At Q-Tech, we use 2D video measuring microscopes, a 3D scanner and a ZEISS O-Inspect, which combines tactile and optical measuring methods. You want to know more about the individual measuring devices? Then you can get more information in this article. 

Basics & Applications

With automated optical measurements, components can be measured within seconds. It is even possible to measure entire surfaces within milliseconds. Thus, optical measurement methods also have an economic advantage over tactile measurement due to the time involved. 

Optical metrology is used in the automotive industry, aerospace industry, medical technology, electrical industry and tool manufacturing. 

The most common applications are the following: 

  • Quality control: The detailed measurement of the components guarantees that the products meet the specific requirements.
  • Reverse engineering: CAD models can be created on the basis of the full-surface recording of the components and thus, for example, spare parts can be reproduced. 
  • Shape analysis: Optical methods allow the shape of workpieces to be analyzed and optimized more easily. 
  • Surface analysis: The measurement of surfaces provides information about the roughness, texture and other properties of a component. 

What optical measurement methods are available?


Let's now take a look at the optical measurement methods. While many are primarily familiar with laser scanning , there are nevertheless a whole range of different optical methods for assessing physical quantities. 

Laser scanning

Due to its film and television presence, laser scanning gained a high degree of recognition, however, it has only a low status in the field of 3D measurement technology.

During the process, a laser beam travels along the surface of the workpiece and the reflection is detected again via a photosensor. In order for the component to be fully detected, either the object or the scanner must be moved.

Since machines usually require calibration, many inspectors prefer to move the object

One of the main areas of application is the above-mentioned reverse engineering. Here, the required objects are scanned and thus the basic building block for the CAD models is laid. Another common use is model printing with additive processes, such as 3D printing

Even private end users can buy an optical measuring device with laser scanning for little money. For example, modern 3D printers are sometimes already equipped with lasers.

Optical metrology 3D

Light runtime

Astronomy was the origin of optical measurement with the time of flight of light. A well-known application here is the distance measurement of celestial bodies. 

This measurement technology is gradually arriving in industry, but cannot yet keep up with the other known methods in component inspection. 

Stripe and pattern projection

In addition to classic metrology, fringe and pattern projection is well known in the industrial sector, especially in car body construction and in the repair of minor sheet metal damage. Here, the optical measuring device projects a pattern onto the component. Even the smallest disturbances to the surface cause the stripes or squares to distort significantly. The inspector can thus easily detect dents and dings and initiate appropriate solutions.

In addition, the tolerance deviations can be made clear by surface measurements. 

Subsequently, dent removal tools are used. In industry, if a tested component has a major tolerance deviation, it is rejected and must be reworked. 

For fringe and pattern projection, one needs a pattern projector, an acquisition camera, an evaluation program and a calibration surface. 

Focus variation

Focus variation is actually more familiar from camera technology, but it is also used in metrology - especially in surface analysis. Measuring roughness and profiles is quick and easy

Focus variation can capture a measurement area at once and does not have to scan it first. This makes it one of the fastest optical measurement methods available. Many optical measuring devices with focus variation are gradually replacing measuring devices from tactile metrology. 

Confocal Metrology & White Light Interferometry

In confocal measurement technology, the test object is illuminated with a very small aperture. The aperture sits on an obliquely arranged mirror. This mirror is used to redirect the reflected light and send it through another straight aperture. 

A sensitive light sensor is located behind the aperture. When the focal point of the light hits the surface, a high light intensity is produced. The whole thing happens when the object is guided through the light source's beam path. 

If the named focal point is above or below, the intensity of the reflection decreases. 

The light fluctuations are detected by a sensor and converted into a measured value

Confocal measurement methods and white light interferometry are ideally suited for the detection of tolerances in the micrometer range

Stereo photography

Stereo photography is a simple form of fringe projection. In this process, a workpiece is photographed simultaneously by two closely spaced cameras. The computer then transforms the digital photos into rendered objects. 

However, stereo photography cannot match the accuracy of fringe projection. Consequently, the industrial relevance of stereo photography is significantly lower. 

However, for the field of face recognition or custom clothing fitting, stereo photography is a very reliable method. 

Measuring tools at Q-Tech

Not all of the above methods are used at Q-Tech. You can find out which measuring tools and methods we use below

2D video microscope (OGP SmartScope Flash 200)

The 2D video microscope from OGP is a fully automatic measuring system that offers extensive measuring possibilities. A characteristic feature of the SmartScope Flash 200 is the lifting bridge, which ensures that the system takes up very little space on the table. 

A built-in LED ringlight provides the perfect flexibility for surface illumination. The whole thing is supported by an LED array backlight. 

ZEISS O-Inspect 

The ZEISS O-Inspect is a combination of optical and tactile sensors. The measuring device offers a large field of view with high image sharpness, fast and precise tactile 3D measurements and optical measurements for sensitive surfaces.

Added to this is the CALYPSO software from ZEISS, which is convincing all along the line thanks to its intuitive operating concept and wide range of functions.   

3D scanner (GOM ATOS Q 8M)

Last but not least, Q-Tech owns the ATOS Q 3D scanner from GOM. This scanner is very versatile and excellently suited for complex measuring and inspection tasks. Even high metrological demands are no problem for the ATOS. 

The success of ATOS sensors lies in precise optoelectronics, robust sensor design and comprehensive software

The lenses can be easily exchanged, providing even more flexible working options. When it comes to small to medium-sized workpieces, no one can beat the ATOS scanner. 

You can find an overview of all our equipment here

Optical metrology - how it works in industry

Advantages of optical measurement technology

Now you know the individual methods of optical measurement technology. The following is a summary of the most important advantages that optical systems bring: 

  • Speed: Entire areas can be measured in fractions of a second. Tactile systems need significantly longer here, as they measure from point to point. 
  • Non-contact performance: Optical systems measure from a distance, which prevents both damage to sensitive components and an influence on the measured value.
  • Precision: The resolution and measurement accuracy of optical systems is usually very high.
  • Flexibility: Optical systems can be used almost anywhere - whether it's quality control or reverse engineering

Optical metrology in the future

Optical metrology will play an increasingly important role in industry in the future. 

This development process is characterized, for example, by the integration of optical measurement systems into manufacturing processes, the use of artificial intelligence to analyze measurement data, and the development of mobile and portable measurement systems.

Conclusion: Optical metrology is an indispensable part of modern industrial processes

Modern optical metrology will support industrial manufacturing processes more and more in the future. It offers high speed, precision and flexibility in the measurement of components.

Our ZEISS O-Inspect and GOM ATOS Q 8 M measuring devices are an illustrative example of optical measuring systems that are very flexible and can thus be used in a variety of industries.