A Posterior Segment Ocular Microsurgical Robot With a Decoupling RCM Mechanism Based on a Minimized Internal Constraint Force Optimization Method

This paper presents a leader-follower robotic system featuring a novel 4-degree-of-freedom (4-DOF) Remote Center of Motion (RCM) mechanism, tailored to address the limitations associated with traditional posterior segment ocular microsurgery. The proposed 4-DOF mechanism employs parallelogram motion replication to relocate the bulky instrument insertion drive from the end-effector to the proximal linkage on the base, minimizing obstruction to the microscope’s field of view and the surgical environment. The mechanism’s orthogonal or coincident arranged degrees of freedom, paired with independent drive units, facilitate calibration and enhance control accuracy. A minimized internal constraint force optimization method was proposed to improve RCM point stability and tip positioning accuracy. The mechanism’s configuration and parameters were optimized through an analytical mechanics model, effectively reducing the constraint force on the internal components under the same external loads, thereby minimizing deformation and maintaining accuracy. To enhance robot compatibility, modular surgical instruments with a quick-change coupler were developed based on the analysis of traditional instruments’ characteristics. The prototype was built and kinematically calibrated to reduce manufacturing and assembly errors and thus improve accuracy. Following kinematic calibration to minimize manufacturing and assembly errors, experimental validation revealed positioning accuracies of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$49~\pm ~23~\mu $ </tex-math></inline-formula>m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22~\pm ~13~\mu $ </tex-math></inline-formula>m, repeatabilities of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~\pm ~10~\mu $ </tex-math></inline-formula>m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9~\pm ~4~\mu $ </tex-math></inline-formula>m, and RCM deviations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13~\pm ~10~\mu $ </tex-math></inline-formula>m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$18~\pm ~11~\mu $ </tex-math></inline-formula>m on the X-Z and Y-Z planes, respectively. The cannulation experiment further demonstrates the prototype’s potential for robot-assisted vitreoretinal microsurgery.