Focus-Variation Shape & roughness measurement in one system. Focus-Variation is an optical technology which is used to perform high resolution 3D surface measurements. Its main component is a precision optics containing various lens systems that can be equipped with different objectives. It combines the small depth of focus of an optical system with vertical scanning to provide topographical and color information from the variation of focus. In other words: It delivers information about form and roughness of a surface in one go, which makes it super-efficient. Basically, Focus-Variation is applicable to surfaces with a large range of different optical reflectance values. As the optical technique is very flexible in terms of using light, typical limitations such as measuring surfaces with strongly varying reflection properties even within the same field of view can be avoided. Samples can vary from shiny to diffuse reflecting, from homogeneous to compound material and from smooth to rough surface properties. Focus-Variation overcomes the aspect of limited measurement capabilities in terms of reflectance by a combination of illumination, controlling the sensor parameters and integrated polarization. Modulated illumination means that the illumination intensity is not constant, but varying. The complex variation of the intensity can be generated by a signal generator. Through the constantly changing intensity far more information is gathered from the samples´ surface. Advanced Focus-Variation is further development of Focus-Variation to measure smooth samples. It combines the functionalities of a roughness measuring instrument and a coordinate measuring machine. Users measure workpieces with steep flanks, varying reflections and structured roughness. Advanced Focus-Variation excels in capturing high-resolution measurements of smooth, reflective and high polished surfaces. Supported by the measurement devices InfiniteFocus G6, µCMM and FocusX, Advanced Focus Variation revolutionizes precision measurement. Bruker Alicona measuring systems are based on the technology of Focus-Variation and combine the functionalities of a surface roughness measurement device and a form measurement system. Each Alicona measuring instrument is a: - surface measuring device - surface roughness measuring system - 3D measuring device for geometrical tolerancing - micro coordinate measuring system. Measuring steep flanks with angles larger than 87° is not a problem at all, and even surfaces with strongly varying reflection properties and greatly varying roughness are measurable. Focus-Variation also allows to measure smooth samples. Plus, users benefit from repeatable, robust and stable measurements. Steep flanks: Light coming from different directions is used to positively influence a measurement. The measurement of the maximum flank angle is not restricted by the numerical aperture of an objective. Depending on the surface users measure surfaces with slope angles up to 87°. True color information: Bruker Alicona´s Focus-Variation provides color information of surfaces in addition to depth information. Users receive a color image with full depth of field which is registered to the 3D points. Varying surface reflections: SmartFlash allows high resolution measurements of materials with varying surface characteristics or reflectivity. Modulated light provides optimal illumination throughout the whole measurement area. Users measure glossy, ground, rough, reflective and diffuse components. Robust against vibrations: For each measurement point Bruker Alicona systems process information not only from image points directly in the focal plane but also from areas out of focus. As focus information is utilized over a larger scan depth, the influence of vibrations on the measurement is reduced to a minimum. Users receive high resolution, traceable, and repeatable measurements even in environments with considerable vibrations. Detailed measurements: Up to 500 million measurement points ensure a meticulously detailed measurement. Measurements with tolerances in the μm and sub-μm range along with large working distance are achievable. The high measurement point density of Focus-Variation enables operators to gain a consistently high lateral and vertical resolution even across high measurement volumes. Traceable measurement of small and often hard to access radii, angles, and roughness are also possible. It’s no exaggeration to give "almost everywhere" as an answer. Focus-Variation is needed for quality assurance in production as well as research and development. The list is quite long: It is used in, e.g., tool and mold making, precision manufacturing, the aerospace and automotive industry, in all kinds of materials science, corrosion and tribology, electronics, and medical device development. Chances are very high that even today, you already used one or more components that were produced by applying Focus-Variation. The technical principle: In contrast to other optical techniques that are limited to coaxial illumination, the max. measurable slope angle is not only dependent on the numerical aperture of the objective. Focus-Variation can be used with a large range of different illumination sources (such as a ring light) which allows the measurement of slope angles exceeding 87°. With a beam splitter mirror, light emitted from a white light source is introduced into the optical path of the system and focused onto the sample via the objective. The light is reflected in several directions as soon as it hits the sample via the objective. All rays emerging from the sample and hitting the objective lens are bundled in the optics and are gathered by a light sensitive sensor behind the beam splitting mirror. To perform a complete detection of the surface with full depth of field, the precision optics is moved vertically along the optical axis while continuously capturing data from the surface. Algorithms convert the acquired sensor data into 3D information and create a true color image with full depth of field. This is achieved by analyzing the variation of focus along the vertical axis. In addition to the scanned height data, Focus-Variation also delivers a color image with full depth of field which is registered to the 3D points. This provides an optical color image which eases measurements as far as the identification and localization of measurement fields or distinctive surface features are concerned. The visual correlation between the optical color image of the samples´ surface and its depth information are often linked to each other and are therefore an essential aspect of meaningful 3D measurement. Since the described technique relies on analyzing the variation of focus it is only applicable to surfaces where the focus varies sufficiently during the vertical scanning process. Surfaces not fulfilling this requirement such as transparent samples or components with only a small local roughness are hardly measurable. Typically, Focus-Variation delivers repeatable measurement results for surfaces with a local Ra of 0.009 μm at a lc of 2 μm. Focus-Variation is used to perform high resolution 3D surface measurement for quality assurance in production as well as research and development activities in the lab. Key applications are surface analysis and characterization in e.g. tool & mold making, precision manufacturing, aerospace, automotive industry, all kinds of materials science, corrosion and tribology, electronics, medical device development. Due to its´ technical specifications the Focus-Variation technique is used for both form and roughness measurements.
