3D force sensors for laparoscopic surgery tool

3D force sensors were developed and integrated in a laparoscope grasping head of the Robin Heart surgery robot to provide additional tactile and force feedback to the surgeon. The Si sensors operate with piezoresistive transduction principle by measuring the stress induced signals of the symmetrically arranged four piezoresistors in a deforming membrane. The chip size was reduced to 1 mm2 by applying deep reactive ion etching (DRIE) for membrane formation. DRIE opens the way to fabricate complex shaped membranes, thereby a monolith force transfer rod protruding over the chip surface could be integrated. This rod increases shear sensitivity of the structure and plays crucial role in tactile sensing. According to the medical and functional requirements the sensors were covered by biocompatible elastic polymer. The effect of elastic cover on the device performance was modelled by coupled finite element simulation to determine the appropriate geometric parameters. Sensors were covered with semi-sphere PDMS (polydimethylsiloxane) polymer and the effect of the elastic coating was studied in terms of sensitivity and response time. Preliminary test of the laparoscopic head integrated in the Robin Heart surgery robot was performed.