Micro gears are applied in an increasing quantity in many applications. Therefore, precise measurements are of growing
importance to ensure their quality. This contribution describes the measurement of gears of a micro planetary gear set
with a tactile probe, a tactile-optical probe, an optical sensor, and computed tomography (CT).
For the tactile measurements, a high precision piezoresistive microprobe was used. A so-called fiber probe was applied
for tactile-optical measurements. This probe applies image processing to determine the position of the tactile probing
element. For all tactile and tactile-optical measurements, single point probing was used. The optical measurements were
carried out with an imaging sensor based on focus variation. Due to limited accessibility, on some gears not all regions
could be measured by the optical sensor and the tactile-optical probe. In contrast to this, with CT the whole part could be
measured with high point density. We used a micro-CT system and carried out measurements with Synchrotron-CT.
All the sensors used deliver measurement data in Cartesian coordinates. It is a challenge to transfer these data into
coordinates in which gear parameters are defined. For this, special attention must be paid to the determination of the gear
axis and to the orientation of the teeth.
The applied procedures are detailed for different micro gears. The comparison between data of different measurements
was carried out successfully. The deviations between the CT data and the tactile or tactile-optical data lie in the range of
only a few micrometers.