Novel Mechanical Actuation of a Modular Laparoscopic Surgical Tool

Abstract

A functional analysis of current laparoscopic surgical technology prompted a redesign of the tools in order to provide multiple functionalities within a single tool. With this redesign came the need for a number of novel mechanisms to actuate and deploy functional tips to the surgical site from their storage locations. In this study we have adopted a multifaceted approach to biomedical device design: functional decomposition to determine problems with the current minimally invasive surgery paradigm, axiomatic design to ensure an efficient design, and quality function deployment to mathematically determine important design criteria. These methods were applied to the design of several novel mechanisms for achieving multifunctionality in a modular surgical instrument. The new actuation mechanism transfers squeezing motion from the hand through a gear train to the distal end of the tool where a pin-slot mechanism actuates the tool tip. The most pronounced change from current technology is the method for rotating the tool’s shaft: rather than a rotary∕rotary interaction using the index finger, a more ergonomic slider mechanism translates linear thumb motion into rotation of the tool’s shaft through a gear train. Finally, rather than locking or unlocking the jaws of the tool using multiple trigger∕ratchet interaction, the new tool uses a binary ratcheting mechanism (similar to a retractable ballpoint pen) to lock or unlock the tool with only one motion. In addition to the actuation mechanisms, the methods for indexing functional tips within the tool and interfacing the tips with a lead screw were redesigned for a modular tool. Rotary indexing of the tool cartridge is done using a Geneva-type mechanism and cam∕follower to provide positive locking once the tip is in place. Transferring the tool tip from the rotary chamber to contact the actuation∕shuttling screw is accomplished using a screw∕wedge assembly to ensure proper attachment. Each of these mechanisms is described and analyzed in detail to show the overall improvement in surgical performance of this novel tool. The benefits identified include multiple functionalities in a single tool, ergonomic benefits of an increased input∕output force scaling, decreased out-of-plane motion required to rotate the tool’s shaft, and decreased cognitive load required to lock and unlock the tool’s jaws.