• deformation
• microsurgery
• plastoelasticity
• robotics
• teleoperation

The field of robotics is rapidly advancing across numerous applications, particularly in the surgical domain, due to its substantial benefits such as enhanced precision, elimination of surgeon tremors, and simplification of otherwise intricate or impossible surgical procedures. A widely employed transmission mechanism for end-effector motion involves the use of polymeric tendons, whose dynamic behaviours have become a subject of extensive research. Notably, when subjected to cyclic force applications at variable speeds, as encountered in practical robotic movements, these tendons exhibit complex dynamic characteristics, including nonlinear elongation, hysteresis, creep, and short- and long-term recovery behaviours.
This study, conducted at Medical Microinstrument Inc. in Pisa, is focused on the transmission system of the teleoperated robot Symani, specifically designed for microsurgery applications where high precision is required. The research aimed to comprehend how the sophisticated nature of the tendons could influence the overall performance of the robot, particularly in terms of modifying its mechanical and geometrical characteristics over time under the application of forces of varying amplitudes and velocities. If tendon elongation is not considered by the controller, errors in the end-effector's position are inevitable. Consequently, a dynamic model is proposed to account for these characteristics, subsequently integrated into the robot's control system, enabling real-time adjustments to the transmission system control input.
To assess performance improvements, tests were conducted using a micro instrument designed for suturing, both with and without the inclusion of the novel compensation strategy. Tests included accuracy assessments and resolution analysis. Despite the instrument's resolution remaining unchanged, accuracy improved on an average of 55% in pitch movements, 24.5% in yaw movements, and 43% in grip movements (open/close degree of freedom). The results underline the importance of considering complex tendon dynamics in both the design and control of robotic systems, particularly in applications demanding high precision, such as microsurgery.