A deflectometric sensor for the on-machine surface form measurement and adaptive manufacturing

Aspherical lenses are usually generated by a multi-axis computer numerically controlled machine and axis guidance errors as well as wear and environmental influences lead to unavoidable form deviations. Therefore, the manufacturing process is often performed iteratively with intermitting measurement steps outside of the manufacturing machine and repositioning the sample into the machine, which is causing additional errors. We present a new deflectometric sensor designed for the machine integration, so that the form measurement is done inside of the manufacturing machine and errors due to the sample removal are avoided. The compact and robust sensor is based on the deflectometry principle. It detects the deflection angle of a focused laser beam on the surface under test and measures the local slope angle of the surface in 2D. By scanning the specimen's surface using the machine axes and integration of the slope angles, the topography can be calculated. The angular measur ement range of +/-9.5° permits the measurement of highly aspheric surfaces, e.g. at a clear aperture of 8 mm a maximum deviation of more than 500 m can be measured at a resolution on the nanometer scale.