L. Doering, J. Frühauf, U. Brand
MICRO FORCE TRANSFER STANDARDS
The measurement of material properties and dimensional metrology are often carried out by mechanical probing using small spherical probing balls. Well-known instruments, such as microhardness measuring instruments, atomic force microscopes, stylus instruments and coordinate measuring machines operate in this way. With increasing miniaturisation and high precision requirements for measurement, these probing systems become ever finer, i.e. the radius of the probing spheres used becomes ever smaller. It therefore is necessary to increase the resolution and accuracy of the measurement. This reduction of the probing sphere diameter leads to the reduction of the probing forces required in order not to destroy the surface of the workpiece to be measured. Small probing forces are needed in particular, when soft materials are measured, i.e., in the ideal case, the probing force should be zero. In reality a force is, however, necessary to deflect the stylus tip and to ensure permanent contact between the stylus tip and object measured. These small probing forces below a few mN therefore have to be measured very exactly. For these purposes, different kinds of silicon bending beams or cantilevers, respectively, have been examined. Two types of micro force sensors were investigated: active and passive sensors. Passive sensors, which consist of calibrated bending beams can be used as micro force calibration standards. Active sensors also consist of Si bending beams but with integrated piezoresistive strain gauges for measuring the beam deflections during probing. Commercially available cantilevers, which were originally produced for application in atomic force microscopes and cantilevers manufactured by the Faculty of Electrical Engineering and Information Technology of the Chemnitz University of Technology were investigated as micro force transfer standards and sensors.
