Implementation of self-sensing SPM cantilevers for nano-force measurement in microrobotics

Micromanipulation tasks have to be solved in the assembly of microsystems, the handling of biological cells and the handling of specimens for scanning electron microscopy. For these applications, we have developed a flexible micromanipulation station, including direct-driven robots a few cubic centimeters small. The robots are able to perform high-precise manipulation and positioning of microobjects. Force-controlled microgripping strategies are now necessary to develop robust microassembly strategies. Microgripping is different from conventional gripping in two ways. First, microparts with dimensions less than 100 microm are often fragile and can easily be damaged during gripping, thus special grasping techniques are needed. Second, the mechanics of manipulation in the microworld are much different than in the macro-world. Part interactions in the microworld are dominated by adhesive forces making it difficult to release parts during manipulation tasks. Several microgrippers that do not employ force feedback have been developed; force-controlled microgrippers are much less common. Grippers with integrated piezoresistive force sensors and with attached strain gauges have been reported. These approaches, however, are limited in their ability to resolve the gripping force. Hence, we are currently integrating self-sensing SPM cantilevers into a gripper of our microrobots. These cantilevers operate by measuring stress-induced electrical resistance changes in an implanted conductive channel in the flexure legs of the cantilever. The real-time force feedback provided by these sensors enables us to better understand the prevailing nano forces and dynamics, what is indispensable for reliable micromanipulation strategies.