A disposable plastic compact wrist for smart minimally invasive surgical tools

This paper describes a new compact bending and disposable (to avoid nosocomial contaminations) plastic wrist for minimally invasive surgery with a large free space for several connections such as electrical wires, fiberoptics and fluidic tubes, etc. It uses small partially locked ball joints to increase the dexterity of surgical tools in all directions contrary to other wrists using several successive orthogonal joints. This compact wrist is a generic concept comprises at least two vertebrae composed of non-attached contacts: plastic plates and balls. Six metal wires drive the position of each vertebra and several other free wires allow the locking of wrist axial rotations. Analytic and finite element simulations allow an evaluation of the mechanical rigidity of the wrist by several parameters: the wire number, diameter, position, mechanical properties and the general geometry of the wrist. The wrist is fabricated with 6 mm biocompatible plastic vertebrae micromachined by low cost water jet cutting. It uses 0.3 mm NiTi super-elastic wires for its mechanical structure which enable two degrees of freedom (DOF) in any directions between -85 degrees and 85 degrees. The two DOFs of the wrist and the DOF of the forceps are driven by a handled basic system using pulleys, 0.5mm Topline® ropes connected to NiTi wires and four RC-servomotors. In the first prototype 6 electrical wires, 2 micro-light emitters and 4 fiberoptics were successfully integrated. We are convinced of the effectiveness of this compact disposable plastic wrist, to be used with a usual or a motorised handled surgical instrument and integrating new functionalities such as electrical/optical/fluidics connections for smart surgical embedded micro-systems like micro-sensors and micro-actuators.