Full 3D acquisition of cylinders and cones within a few seconds

Injection nozzles and valve needles demand a fast and accurate measurement of the outer and inner shape of the surface. A standard white-light interferometer cannot acquire the complete surface of cylindrical or conical objects in one single measurement. We modified the white-light interferometer to measure in cylindrical coordinates. For cylindrical objects a 90° conical mirror is used to illuminate and to observe the measured object. For conical objects the angle of the conical mirror has to be properly adapted. To measure the inner surface, specifically the conical end of the injector nozzle hole, we developed a micro-conical mirror in cooperation with the “Institut für Werkzeugmaschinen und Fabrikbetrieb” IWF, TU Berlin. Experiments display that the alignment of the object and of the conical mirror is uncritical and sub-wavelength accuracy can be achieved. It should be noted that the imaging of the object surface via the conical mirror leads to geometrical distortion, but there are only minor geometrical aberrations that do not affect the measurement. The measurement of the full surface can be done in a few seconds.