Micro-Force sensor by active control of a comb-drive

This article describes an active force sensor with an accuracy of 0.4 μN over a large range [-400 to 400] μN. The mechanical structure, through a fiber suspension arrangement, provides exactly one degree of freedom. This design allows for a precise displacement sensing by a laser optical lever. The force sensing principle is based on the active control of an electrostatic bi-polar actuator. A meso-scale prototype has been built as proof-of-concept and an especially designed controller allows for high precision measurements on a large range. The system is validated by measuring both pull-in and pull-off forces during an approach-retract cycle on water droplet. Both phenomena, although differing by an order of magnitude in amplitude, are correctly assessed.