Design Concept of Hybrid Instrument for Laparoscopic Surgery and Its Verification Using Scale Model Test

This paper proposes a new design concept of hybrid instrument for single-port laparoscopic surgery (SPLS) and a new method of verification using a scaled-up prototype based on the principle of elastic similarity. The proposed concept is a hand-held instrument that uses a tendon-gear mechanism for dexterous movement of its end-effector and servomotors with flexible tendon-sheath transmission to maintain the dexterity by compensating the loss of output angle from tendon elongation during the manual operation. The kinematic relationship of the tendon-gear mechanism was derived mathematically, and the ratio of external moment to resistive flexural stiffness of the articulating joint was matched between the real-sized model and the large-scale prototype. Our scale model tests have shown good agreement between their input-output relationships under the equivalent loading conditions, and thus verified the validity of similarity analysis. Also, the proof-of-concept experiments have demonstrated the functionality of output loss compensation of the hybrid instrument. Our methodology can be used to simplify and speed up the prototype development process for SPLS by avoiding miniaturization challenges such as high precision manufacturing, which is costly and time-consuming.