Bruker Alicona's measurement systems are based on the principle of Focus-Variation. This is a high-resolution, optical 3D measurement technology. However, Focus-Variation is not the only optical technology that can solve dimensional measurement tasks. Precise and non-contact measurement is indispensable for a wide range of applications. In this blog article, we present the five most important optical measurement technologies and highlight their advantages and disadvantages: White light interferometry, confocal light, 3D scanner, measuring microscope and, of course, Focus-Variation.
How to choose between White Light Interferometer, 3D Scan or Focus-Variation?
1. White light interferometry: precision at nanometer level
White light interferometry (WLI) is a high-precision measurement technique that uses light waves to detect surface structures. It can make the finest details visible through interference patterns.
Advantages of white light interferometry
- Highest precision: With the ability to perform measurements in the nanometer range, white light interferometry sets standards in accuracy.
- Nothing is too smooth: from highly polished to medium roughness. The white light interferometer can even measure the roughness of a mirror. This measurement technology is therefore particularly suitable for wafers in the semiconductor industry
Disadvantages of white light interferometry
- Vibration-sensitive: High-precision white light interferometers require actively vibration-damped tables. This makes the measuring systems unsuitable for use in harsh production environments.
- Limited range of applications: Rough surfaces, steep edges, complex shapes and structures are a problem for the white light interferometer. Or rather the user, as it is difficult to find the right measurement settings. Shape and position measurements are hardly possible.
- Complex handling and data analysis: The small working distances of the standard lenses make measuring complicated. Interpreting the results also requires specialist knowledge.
2. Confocal sensors: detailed imaging
Confocal microscopy uses focused light to produce sharp, high-resolution images of surfaces. In the process, out-of-focus light is blocked out, resulting in a better depth of field.
Advantages of confocal sensors
- High resolution: Confocal light makes it possible to capture the finest details and structures.
- Excellent depth of field: ideal for examining three-dimensional structures.
- Versatile use: Particularly suitable for fluorescent samples and a wide range of applications in biology and materials science.
Disadvantages of confocal microscopy
- Time-consuming: The method becomes really time-consuming when recording large areas.
- Complicated measurement: As with the white light interferometer, the working distances of the standard lenses are small, which makes measuring complex.
- Limited range of applications: Confocal microscopy is also very limited when it comes to shape and position measurements.
- Vibration sensitivity: For accurate measurement results, confocal sensors need a low-vibration environment
3. 3D Scanner
3D scanners are based on a technology that digitizes three-dimensional bodies. They use light or lasers to depict the shape of an object. This technology is particularly useful for measuring complex structures. The spatial data of objects is recorded without contact. A 3D scanner enables the exact representation of the geometry of a real object in a digital environment. The information obtained from different angles is combined and processed to create digital models. There are several types of 3D scanners. In optical metrology, fringe projectors and laser triangulation are particularly important.
Structured Light (Fringe projection): Fast and versatile
A fringe or structured light projector is a 3D scanner that projects a stripe pattern onto the object and analyzes the distortions of this pattern to reconstruct the surface.
Advantages of the fringe projector
- Fast measurements: Enables rapid detection of large areas.
- User-friendly: Simple operation and implementation.
- Versatility: Suitable for various materials and surfaces.
Disadvantages of the fringe projection/structured light technology
- Accuracy: Compared to other technologies, the structured projector does not exactly shine with high precision.
- High preparation and cleaning effort: all non-matt surfaces must be sprayed to enable measurement
- Light-sensitive: Ambient light and reflections affect the structured light to the point of making it unusable.
Laser triangulation: precise and fast
The triangulation method is based on a principle in which a laser beam is projected onto the object and the reflection is measured in order to calculate the distance. This is also a 3D scanner.
Advantages of laser triangulation
- Speed: Enables fast data acquisition.
- Versatility: Can be used on a wide variety of materials and surfaces.
- Production capability: Simple geometries can be measured directly on the production line using inline sensors.
Disadvantages of the triangulation method
- Precision: Laser triangulation is not precise enough for shape and position tolerances in the hundredths range.
- Effort for complex components: Problems with shadowing make a complete 3D measurement of complex components only possible with a great deal of effort.
- Reflective surfaces: Laser triangulation has difficulties with highly reflective surfaces.
4. Measuring microscope: Precise at micrometer level
A measuring microscope combines optical magnification with measuring functions and is used for the precise measurement of small structures. Measuring microscopes can use various measuring methods, such as electronic contact measurement or optical projectors. Two main principles play a role in non-contact dimensional measurement: the transmitted light projection and the reflected light projection.
Advantages of measuring microscopy
- High resolution: Measuring microscopes enable the examination of details in the micrometer range.
- Quick inspection: Visual inspection is quick and does not require any time-consuming preparation.
- Versatility: Optical microscopes can be used for various materials and applications.
Disadvantages of the measuring microscope
- Limited depth of field: At high magnifications, the depth of field may be limited.
- Dependence on light: The quality of the lighting influences the image quality.
- Limited magnification: Optical microscopes are limited in their maximum magnification.
- Subjectivity: The interpretation of the images can be subjective and depend on the user's experience.
Transmitted light projector: A transmitted light microscope uses a light source that shines on the object from below.
Reflected light projector: In contrast, a reflected light microscope uses a light source that is directed at the object from above. This provides a better depth of field. It is often used for surface inspection and quality control.
The choice between transmitted light and reflected light microscopes depends on the type of sample and the specific measurement requirements. Many measuring microscopes incorporate both technologies. Both projectors offer different advantages and can be used in different applications.
5. Focus-Variation: precision and versatility combined
Focus-Variation is an advanced measurement technique based on analyzing changes in focus to capture the topography of a surface. This method offers several advantages:
- High accuracy: Focus-Variation enables precise measurements even on complex surfaces. Unlike white light interferometry or confocal sensors, for example, Focus-Variation can also measure really steep edges.
- Versatility: It is suitable for a wide range of materials and surfaces, from rough to smooth textures.
- It is suitable for the evaluation of form and position tolerances as well as roughness parameters.
- Speed: Data is recorded and analyzed quickly and efficiently.
If you want to find out more about the Focus-Variation, you can read about it here.
Bruker Alicona: front runner in Focus-Variation
Bruker Alicona, as a leading supplier of optical measurement systems, uses Focus-Variation technology, which has been further developed into Advanced Focus-Variation. For special geometries and complex shapes, the Focus Probing and Vertical Focus Probing technologies allow surfaces with angles equal to or even greater than 90 degrees to be optically probed laterally. Bruker Alicona's systems offer outstanding precision and reliability and are capable of handling complex measurement tasks in manufacturing and quality control. The measurement devices combine the advantages of Focus-Variation with user-friendly software and robust design, making them a first-class choice for industrial applications.
Overall, the various optical measurement technologies offer a wide range of options for detecting and analyzing surfaces and structures. The choice of the right technology depends on the specific requirements of the application, including the required accuracy, speed and material properties.
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