A Rigid Mechanism with Uniform, Variable Curvature

For minimally invasive surgery, accessing remote locations deep in the intestines, lungs, nasal cavities, and vascular system requires elongated tools that follow a nonlinear path-- a challenge for most rigid surgical tools. Some mechanism designs can withstand high-magnitude forces but are limited in their maneuverability. Others can have a wide range of motion but perform poorly while under high-magnitude force loads. The presented tendon-driven, crossed four-bar mechanism, provides both the dexterity and range of freedom needed for various hard-tissue procedures in minimally invasive surgery. The mechanism, with a set of cross bars and top and bottom bases each having the same length, can be stacked in parallel with multiple copies of itself to produce a circular arc about its vertical centerline. What makes this mechanism unique from other developed designs is that it can withstand high force loads without deformation and can produce uniform, variable curvature motion while utilizing only one degree of freedom. Using four model modules stacked together with a total length of 30 mm, the module prototype could withstand an external load of 0.2 newtons without any significant deflection while in various positions.