A multi-modal fully compliant mechanism with tunable force transmission for laparoscopic grasping

Compliant mechanisms are flexible devices that achieve motion and force transmission through material deformation. Compliant design can tailor a mechanism's output motion and/or force by controlling material selection and geometric properties. With access to a growing selection of materials and manufacturing processes, compliant mechanism design can incorporate nonlinear elastic theories to achieve unique output behaviors that are unobtainable in conventional mechanism design. This work experimentally verifies a computational design tool for developing a patented, fully compliant, multi-modal mechanism for laparoscopic tissue grasping with nonlinear force transmission capabilities. The computational design tool is used to perform a sensitivity analysis to quantify the fine-tunability of force transmission relative to the mechanism's effective length. Results demonstrate that computational model predict the nonlinear force transmission behavior of the multi-modal mechanism, which acts as a low-pass filter to absorb peak loads beyond a prescribed critical threshold value and can be tuned between 4.44N and 8.50N. A negative stiffness behavior is generated via snap-thru beam buckling to deliver a tactile ‘click’ sensation that can be felt at the instrument handle, which can be fine-tuned between 74.06N and 145.26N concerning the direct actuation force. The authors reflect on the mechanism's multi-modal properties for handheld laparoscopic atraumatic tissue gripping. Validation procedures that establish this device's commercial and or clinical viability is considered future work.