白色光干渉計
白色光干渉計は、測定物からの反射光と参照光が重ね合わされたときに発生する干渉縞を利用しています。
測定原理は、マイクロレンジのコヒーレンス長を有する光源を含む光学系(画像)をもつマイケルソン干渉計の原理に基づいています。まず白色光ビームは、ビームスプリッタで測定ビームと参照ビームに分割されます。測定ビームは、測定物に照射され、参照ビームは参照用ミラーに照射されます。それぞれの反射光はカメラにおいて再結像ます。
測定アーム上の測定ポイントへの光路長が、参照アーム上の光路長と同じとき、光源のスペクトルのすべての波長に干渉による強め合いが起こり、その測定ポイントのカメラピクセルの明暗度は高くなります。2つの光路長が異なるときは、カメラピクセルの明暗度は大幅に低下します。 その結果、カメラは2つの光路長が等しい測定ポイントのみを記録します。
テレセントリック光学系を有する測定機器を使用すると、単一のパスで迅速に広い範囲の表面形状を測定することができます。マイケルソン干渉計がベースの顕微鏡システムは高い横分解能を必要とする測定に適しています。

クロマティック共焦技術
クロマティック共焦点センサTopSensはクロマティック共焦原理を用いて距離と厚さを非接触で測定するセンサです。クロマティック共焦光学系とは、測定光の焦点位置に測定面があるとき、測定面からの反射光の焦点位置が検出器上になるよう設計された光学系であるため、ほぼ全ての反射光がピンホールを通過し検出器に到達します。この原理により、高い分解能と、信頼性、再現性を実現しています。

Flatness is often decisively important for functional surfaces, with examples including components with sealing surfaces used in pressure and vacuum technology, as well as transparent films for displays, semiconductor elements, metal surfaces and ceramic surfaces. Determining percentage contact areas is a simple and reliable process too. In this context, the TopMap systems allow you to measure large surface areas and thus get fast, complete characterization of the workpiece.

Polytec is a world leader in technology for optical topographic measurement of large areas with nanometer precision. Determining parallelism, flatness, radii, steps, angles and other parameters are typical tasks for this technology. The areas to be examined are often situated in subjacent holes or differ a great deal in terms of height. But this is an easy task for Polytec’s systems in contrast to other optical measuring methods, such as coherent interferometry.
In many cases, the complete topography of a workpiece or object has to be checked, as is the case, for example, with the shock absorber component shown here or with other precision workpieces in the automotive industry, in aerospace development or in precision mechanics. Ceramic components, imprints, safety features and even forensic evidence can be analyzed with nanometer accuracy using white-light interferometry. Also, the demands placed on the warping and deformation of components such as printed circuit boards are forever growing as dimensions continue to shrink.

Very often, mechanical designs for workpieces include specifications for defined parameters such as roughness or ripple. White-light interferometers can acquire 3D profiles that require a very long measuring time if acquired using tactile processes within a few seconds, particularly for flat parameters. Such parameters – take the percentage contact area or frequency distributions, for example – can be determined quickly and easily. Roughness can be optically determined too, but the values can deviate from the results of tactile measurements to which the drawing dimensions and standards often refer. However, new guidelines for calibrating white-light interferometers give the user the assurance that the measured values can be traced back to calibration standards. Optical measurements also make roughness parameters available. Often, for instance, it is sufficient to decide whether the surface of e.g. dynamic sealing surfaces is too rough – which would lead to high friction losses – or too smooth, which could result in excessive adhesion.

A large vertical adjustment range is often the key to determining parallelism, height differences or angles between several surfaces. The TopMap series offers adjustment ranges of up to 70 mm, or 50 mm that can be used to measure surfaces that are separated from one another by large steps or are situated inside holes. The TopMap systems’ telecentric light beam path avoids shadowing effects.

Surface metrology integrated into production lines are highly effective. Testing samples at an early stage of the production cycle and identifying trends can significantly reduce production costs. White-light interferometers of the TopMap series are suited to use in a metrology chamber, located near the production line or installed directly in-line. The TopMap In.Line is the dedicated measuring system for production testing right in the manufacturing process. The compact sensor can be used in various mounting configurations in the production line and measures preset specifications like flatness or waviness within short cycle times and with complete coverage.

Determining the amount of material removed plays a key role when it comes to wear measurements. In this situation, the surfaces are often very jagged and the light reflected back shows great intensity differences. The SmartSurface scanning technology incorporated into the TopMap systems guarantees optimum results in such cases, too. Wear and tear studies are also traditional tasks for topography measurements. Examples of such tasks include performing a root cause analysis when brake disks have suffered wear and tear.

In industrial production, compliance with specified tolerances has to be checked as often as possible. This helps to ensure that defective parts are eliminated before any further processing steps are taken and that unnecessary costs are avoided. White-light interferometers can be used to quickly examine large areas of many surfaces for the number of defects, form deviations, ejections, missing connections or break-offs. Processes can be permanently or randomly monitored too. In many cases, the complete topography of a workpiece or object has to be checked.

NC machines often have to be properly adjusted to ensure that parts are manufactured to the required flatness and curvature values. Checking workpieces at an early stage during machine set-up helps to save both time and money. During this process, the relevant parameters are checked before production is started and the processing machines’ settings are optimized. Machine operation can also be monitored with ease.

Basic Priciples Scanning White-Light Interferometry
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