Analysis of a Micro-scale, Tri-axial, Capacitive-based, Differential Force Sensor for Haptic Feedback System in Robotic Surgery
It is known that the absence of tactile feedback in robotic surgery represents a limiting factor to surgeons. In effect, the lack of tactile feedback in robotic surgical tools is closely associated with tissue damage. This is especially true among novice surgeons who, not having surgical tools that measure compressive sensing, apply excessive force causing tissue crush injuries. Additionally, the lack of tactile feedback in the shear directions lead to additional problems, such as breaking of sutures due to excessive pull forces. In view of the lack of tactile feedback, our efforts have been focused on developing a highly sensitive micro-scale, tri-axial, capacitive-based, differential force sensor. To this end, we provide relevant derivations to single-element, multi-axis capacitive sensing including an illustrative discussion on capacitive pressure sensor (CPS) theory. We begin our discussion on CPS theory with the well-known parallel plate capacitor to illustrate key physical concepts and move on to more complex structures, such as capacitors with asymmetrical surface areas under deformation. Whenever possible, we provide explicit capacitance expressions for these last structures and demonstrate that such expressions reduce to more familiar ones. To ensure the validity of our theoretical calculations, we have also provided results obtained from COMSOL Multiphysics simulations. It is worth mentioning that for our theoretical calculations, we have only considered deformations in the downward direction as a result of external forces applied to the top surface of the CPS model so as to facilitate the evaluation of capacitance expressions. For the COMSOL Multiphysics simulations of our proposed capacitive force sensor (CFS) model, on the other hand, no restrictions are imposed on the direction of deformation. The design, including sensor location and performance criteria, of our current CFS model is also considered as well as its working principle.