Getting the measure of technical mirrors

THE SURFACE characterisation of technical mirrors is of critical importance for manufacturers. In many cases, quality is still assessed by the human eye. As this work requires maximum concentration, it depends on the ability of the inspector on the day and leads to eye fatigue over time. As a result, employee performance fluctuates and not all existing parameters are reliably recognised. This means that reproducible quality is only possible to a limited extent.

Micro-Epsilon’s reflectCONTROL measurement system enables automated surface inspection of reflective or shiny objects with consistently high quality. The results are output in the form of 2D images and a 3D point cloud.

Advantages of 3D technology

In particular, with flat surfaces, the reflectCONTROL technology impresses with its high measuring rates and nanometer accuracies. The 3D sensor uses the principle of phase-measuring deflectometry. It is characterised in particular by its extremely high z-axis resolution in the nanometer range. In combination with its large measuring range of approximately 170 mm x 160 mm, up to five million data points of the surface to be measured can be recorded within a few seconds.

The reflectCONTROL sensor is used, for example, for 3D shape detection of wafers in semiconductor production, quality inspection of flat glass, e.g. in smartphone production, and surface inspection of head-up displays.

In many cases, manufacturers of technical mirrors use sensor solutions in which mirrors with a diameter of 100mm are measured using around 16 sensors. The resulting measuring points are interpolated across the mirror surface to determine the respective deformation. These measuring methods are often only suitable to a limited extent for quality specifications in the nanometer range. The reflectCONTROL sensor, on the other hand, captures the surface with up to five million data points, allowing the measuring object to be precisely reconstructed.

Phase-measuring deflectometry

The reflectCONTROL sensor works according to the principle of phase-measuring deflectometry. The method is particularly suitable for high precision defect detection and three-dimensional geometrical detection of flat reflective objects.

Deflectometry systems are superior to other optical methods in that the required local curvature, intensity and amplitude data are available over the entire area captured by the camera. The advantage of the stereo measuring system lies in the simultaneous image acquisition of two cameras from different directions. The combined evaluation of the data from both cameras enables a 3D reconstruction of the measuring object with nanometer precision.

For more information:

www.micro-epsilon.co.uk

Tel: 0151 355 6070