Abstract: A scanning head (12) for a surface measuring machine has a probe tip (30), which is supported by a probe tip support lever (18) so that it can be deflected perpendicularly to the reference surface (82). Incorporated between the probe tip (30) and a rigid section of the probe tip support lever (18) is a force sensor (34), whereof the output signal serves as an actual value of a control circuit (56 to 60), which controls a magnetic servo motor (44, 46), which exerts a variable additional force, to be added to the force of a tension spring (42), on the probe tip support lever (18), the whole so that the contact pressure of the probe tip (30) is kept constant irrespective of the surface contour.

Abstract: An optical thickness measuring instrument for transparent work-piece, in particular glass plates and transparent films, consists of a scanning head (10) with a servo-controlled measuring lens (24), a mirror (12) arranged perpendicularly to the axis of the latter and means (66 to 72) for positioning the work-piece (64) in parallel above the mirror (12). The servo control adjusts the measuring lens (24) so that a measuring light source (34) is focussed on the surface of the mirror. For this purpose, the measuring lens (24) must be adjusted by the associated servo drive (18, 20) depending on the thickness of the work-piece (64). The electrically measured (40) adjustment displacement of the measuring lens (24) is a measurement of the thickness of the work-piece (64). (FIG. 1).