Fully mechanical motion-scaling instrument for microsurgery assistance: design improvement for enhancing the dynamic performance

Robot assistance can improve the outcome of microsurgery by scaling down the surgeon's hand motions. However, the high cost of surgical robots has prevented their use in small hospitals or medical facilities in several developing countries. As a novel alternative, a fully mechanical motion-scaling instrument, which can be operated without computers and motors, was proposed based on the pantograph mechanism. However, it had several problems owing to the cumbersome and heavy structures during the prototype test. This study aims to solve the problems found in the first design and prove the advantages of the improvement, based on the design and performance criteria. The pantograph structure was simplified, and the gravity compensation method was modified to reduce inertia by using a constant force spring instead of a counter-mass. The improvement was computationally predicted using a mathematical model, and the results were verified through trajectory measurements in a micro-positioning task. Finally, the evaluation of dynamic performance is quantitatively presented through iterative positioning tasks.