Such an optical system is described in German Published Patent Application No. 198 08 273. With this known measuring system, having as its essential component a fiber optic short coherent multi-wavelength heterodyne interferometer, a measuring probe directed at the object surface, and a reference probe to be directed at a plane table on which the component having the surface is mounted, are connected to a beam delivery section having a short coherent broadband light source and a modulation interferometer receiving the light therefrom. Position relationships and changes between the object surface and the bearing device are detectable with this probe system of measuring probe and reference probe and may be taken into account during the surface measuring procedures to reduce and/or rule out measuring errors resulting from such deviations in position. However, other relative local changes between the outputs of the probe system points on the surface, e.g., inaccuracies in the probe guidance or relative movements between probe and component in various degrees of freedom during the measuring procedure, may have effects on measurement of the surface geometry of a component or multiple components in a fixed positional relationship to one another, e.g., distance or roughness or roundness. Such influencing parameters on the measuring procedures are difficult to rule out, in particular in measurements of shape and/or distance related to the manufacturing process.
Today mainly pneumatic measurement methods are used for a robust measurement of shape and distance and/or diameter of guide bores, for example, that will have relevance for the manufacturing process. However, the precision of these methods is technically limited and will probably not be able to comply with increased tolerance demands in the future. However, for high-precision measurements, high-resolution measurement methods in the nanometer range are needed, but such technology may currently be installed only in precision measuring laboratories having vibration isolation.
Mainly punctiform distance sensors are used for the high-resolution determination of shape and diameter on guide bores; the measuring heads of these distance sensors are capable of very accurate determination of the distance from the surface of a component to a reference point. Such punctiform distance sensors must essentially be combined with a shape-measuring machine which guides the sensor mechanically along a defined path over the surface of the component to be scanned to measure the shape of the component. The accuracy of such measurement methods is based essentially on the precision in guidance and the mechanical stability of the shape-measuring machines.
Optical sensors, in particular those that operate by an interferometric principle, have recently made advances as punctiform distance sensors replacing tactile scanners because of the non-contact measurement principle and the resulting advantages. Of the interferometric sensors, in particular the multi-wavelength heterodyne interferometer having a short coherent light source is a rapid punctiform measurement method that has already been tested industrially and is capable of measuring rough industrial surfaces. However, confocal measurement methods are also known as optical measuring systems.