Cable Vibration-Based Tension Sensing for Cable-Driven Articulated Forceps

Force sensing for multi-degree-of-freedom articulated forceps is challenging for several reasons, including size constraints, the harsh environment inside the patient’s body, and sterilizability. This paper proposes a sensing method that overcomes the fragility and production cost disadvantages of conventional force/tension sensors that use flexure elements. Vibration-based tension sensing induced vibrations in forceps’ driving cables. The resulting fundamental frequencies were measured using photo interrupters. A rotating shaft was mounted on an axis parallel to cables suspended between two pulleys, with a small protrusion in the radial direction that plucked at the middle of those concentrically arranged cables. Cable tensions were estimated from the measured fundamental frequencies with satisfactory accuracy, repeatability, and vibration-to-noise magnitude ratio. The plucking negatively affects the wear of the protrusion and cables while inducing undesired vibration transmission and changes in the contact/grasping force at the forceps tip. A nylon protrusion and nylon-coated cables were used because nylon is wear-resistant, low-friction, biocompatible, and sterilizable. The results revealed minimal wear after 106 plucking cycles, minimal vibration transmissions and changes in contact force, and little interference with the photo interrupter signal from the plucking on another cable.